This was written for the lovely bransonvevo (bleulily on tumblr) for the S/T Secret Valentine exchange! She gave me a wonderful prompt for a Regency AU where Sybil and Tom are in a secret relationship and pass love letters back and forth, and I ran with it. I love the Regency era may be a little bit too much so this was a serious joy to write.

(Plus it gave me an excuse to sneak in Jane Austen and spies, so I can't complain.)

London, 1812

They meet for the first time at a ball.

It's Sybil's first season and the past month has been a flurry of tailor's appointments, dance lessons, and teas with nearly every one of her mother's acquaintances. Sybil can't wait for the evening to be over, if only so the terrible drama leading up to its achievement will finally be over. Most girls are terrified at the thought of curtseying in front of the king, but she isn't terribly concerned—she's been curtseying to Lord So-And-So and Duchess This-And-That for as long as she can remember.

What she's excited about is the freedom; to finally be able to attend balls with her sisters instead of spending the evening at home with Anna and Bates, playing chess and reading books by the fireplace. Dancing is one of the greatest joys in the youngest Crawley's life, and she intends to enjoy every second of it.

(It doesn't hurt that her presentation frock is beautiful, either.)

The night of her debut, her mother and Mary fuss over her as if she's about to be married, which, in a sense Sybil supposes she is—after all, is this not the whole point of the season? Frankly, she finds it quite unnecessary, but everyone refuses to entertain the notion of Sybil getting dressed without supervision—Granny, even, hovers by the fireplace giving her opinions on everything from the way Anna laces the corset (not tight enough) to the pins she's chosen for her hair ("Far too gaudy. You aren't a gypsy, Sybil.").

Everyone agrees in the end that she looks beautiful and Sybil feels a thrill run up her spine when she catches a glimpse of herself in the mirror. The gown is a masterpiece: violet silk with an empire waist and a long flowing skirt. A delicate sash of silver lace trims her waist and trails the length of the skirt like a tail, tiny glittering peals scattered across it like dew drops in a spider's web. The neckline is trimmed with a neat line of pearls to match the strings caught in her dark curls, and a delicate fan of silver lace rises from the square neck—to "cover all right parts" the dressmaker said. Her mother has given her a necklace: a string of pearls with a single teardrop-shaped diamond pendant, and Mary bought her a new pair of white satin gloves with pearl buttons along the inseams for the occasion. Edith slips a single white rose into her hair and Rose, who has her debut next year, gives her a kiss on the cheek for luck. Even Granny smiles and tells her that she looks beautiful.

This is it. This is the moment she has been waiting for her whole life. Not the presentation to the king, which happened two days previously in a white dress not nearly as beautiful as this one and was exceptionally boring, but her first night out socialising with the ton, the first night she can fill her dance card up with suitors' names and drink punch and stay out until far past a respectable hour having an absolutely wonderful time.

"Almack's isn't quite so exciting, darling," Mary says crisply, as the carriage rattles through the streets of London. "The gentlemen aren't all white knights—most of them are hardly gentlemen."

"Mary," the Countess scolds.

Edith lifts one shoulder in a shrug, smoothing her gloved hands over the skirt of her gown, a muted peach satin. "It is true, Mama. There are far too many young men out in society who don't act very much like gentlemen at all."

"As long as they don't step on my feet I really don't see what there is to object about," Sybil replies, trying not to sound too excited. "I've been waiting eighteen years for the chance to dance all night and I'm hardly about to let some old-fashioned ideas get in my way."

"Sybil!"

Mary rolls her eyes. "Oh, honestly, Mama, you know she doesn't mean it. Sybil gets more joy out of your reactions to her suggestions of rebellion than she does from the things themselves."

Sybil scowls. She does mean what she says, she only hasn't had the power to do much about it until now.

"Sybil's perfectly welcome to spend the whole evening dancing if she choses to and there's no shame in admitting it." Edith shoots Mary a sharp look that Sybil knows well; an argument looms on the horizon. "She isn't obligated to get betrothed tonight."

"Certainly not, though I expect she'll do better than you," Mary retorts.

"I hardly think there are suitors lining up at the door waiting for your hand in marriage," Edith snaps, pink spots blossoming on her cheeks. "As I recall, the last man you were betrothed to died in his bed."

"Edith," Lady Grantham hisses.

(Sybil has never been so glad to arrive at their destination in her life.)

She dances the first waltz with Tom Bellasis, whose company she has always enjoyed, even if he is a little mild-mannered. Larry Grey takes the quadrille and the gavotte, much to her chagrin—she's never particularly enjoyed his company but their parents are very well acquainted and it would be terribly rude to turn him down, particularly when her card isn't filled. He steps on her toes twice, and spend both dances discussing the many benefits of his vast fortune, implying heavily that Sybil would benefit very much from a union with him. Pretending to be interested in what he has to say is exhausting, so Sybil makes her excuses, pretending to have seen an old friend on the other side of the room. Larry, mercifully, has no interest in following her.

Mary has often complained about the punch at Almack's—it's either too sweet or too tart, for nothing is ever good enough to satisfy Contrary Mary—but Sybil finds it deliciously refreshing after three sets on the dance floor. As lovely as it is to be able to take to the floor with the young men of the ton, it is equally pleasurable to watch couples whirl by in their tails and fine silks, or to listen to the group of young ladies clustered by the table gossiping about who will be married off by the end of the season.

Sybil is so engrossed in the riveting discussion of Lady Mabel Layne-Fox's budding romance with Sir Tony Gillingham that she doesn't see the group of boisterous young men cutting their way through the crowd to the terrace behind her. The ladies dissolve into fits of giggles upon seeing them, raising fans and eyebrows in expressions of demure seduction, but the men are oblivious, laughing heartily and clapping one another on the back in an expression of mutual camaraderie.

It would be quite lovely if one of the gentlemen in question hadn't plowed into to Sybil as if she weren't there, knocking her off-balance and sending her glass of punch tumbling towards the floor, without so much as a backward glance.

Sybil, manages to right herself but the glass of punch, it seems, isn't quite so fortunate. She waits for the inevitable crash of crystal against the floor, but it never comes.

"Looking for this?"

Her punch glass, miraculously unharmed, sits in the outstretched hand of a young man in tails. He's quite handsome: clean shaven, square jaw, neatly parted brown hair, but what catches Sybil's attention are his eyes: piercing blue and glimmering with a mirth so magnetic she finds it impossible to look away.

"I— You're very quick with your fingers, sir," Sybil says, trying to will the flush away from her cheeks as she accepts the glass from him. (Why must he affect her so? They've only just met.)

Her rescuer grins carelessly. "An occupational hazard, my lady."

If Sybil were the heroine in a romance novel, she would have some witty retort. "How do you know I'm a lady?" is what tumbles out instead.

"Why with a face and a gown so lovely? You must have good breeding. And to be frequenting Almack's, no less."

Sybil smiles. Mary always says she musn't give in so easily to men because it gives them the upper hand, but there's something about his eager, open charm that immediately puts her at ease. "Then you must be at least a lord. Or perhaps a duke? You've the nose for it."

(His nose is most excellent; Romanesque, like a foreign prince.)

He smiles ruefully. "I wish I could aspire to such a nobel calm, but alas, I am only a politician."

"A politician? How exciting!" Mary says politicians are the most despicable sort of men, but that's only because she still adamantly believes she isn't in love with one Matthew Crawley, MP. Most of what Mary says is talk in either case, neither Edith nor Sybil take much stock in her advice, though Edith loves to quibble about it. Sybil loves politicians—she'd gladly spend an afternoon discussing parliamentary bills and civil rights movements and the war with Matthew than drinking tea and gossiping about the latest court scandal.

"Perhaps, if I were in fact a politician, but I'm only an aide. Run errands and such—nothing terribly exciting."

"It sounds terribly exciting to me," Sybil replies stubbornly. "I should love to be in Parliament, if I had the chance."

Tom—she finds out his name later, Tom Branson, who works as Matthew's aid (quite the coincidence) and is from Ireland originally—as it turns out, has many exciting stories to share about politics, which he does as they dance the next three sets together. He begs off a fourth—"It's not that I don't enjoy dancing with you, m'lady, but folk are starting to stare."—and they take refuge on the terrace outside instead. Sybil hasn't enjoyed conversation this much in a long time, not even with Tom Bellasis, who while very kind, is quite dull in comparison.

It's a bittersweet parting when Edith finally comes to fetch her an hour or so later, but they make arrangements to meet for tea the next afternoon at a teahouse near Parliament and Tom promises to write to her when she returns to Downton.

"A successful first night out, I presume?" Edith says as they climb into the awaiting carriage.

Sybil pointedly ignores the smirk pulling at the corner of her sister's mouth.

January 17th 1813

My darling,

I had the strangest dream last night. Though strange might perhaps be the wrong word—thrilling is more apt a description. It woke me from a dead sleep and I felt awfully flustered and warm all over, as if I had just emerged from a very hot bath. I'm not even sure I should be telling you these things—it certainly isn't appropriate for ladies to be discussing them—but I miss you so and I want to be able to give you some piece of myself to keep with you in France. I've never had a dream like this before, but I daresay, if you were to touch me the way you did in it when we are together, I should likely burst into flames.

I hope you don't find it too shocking—though I hardly think you will, wicked man that you are—and I can only hope that we are reunited soon so that we might perhaps explore the possibility of turning some of these fantasies into reality.

Yours eternally,

S.

P.S. I cannot believe what I have written. My cheeks are burning just from reading this letter, so I had better post it quickly before I change my mind and throw it in the fire. I can only hope that it doesn't fall into the wrong hands before reaching you, else Rose will be in some serious trouble!

May 25, 1814

S,

You cannot possibly know how beautiful you looked last evening at Almack's. I wish we could have spent more time together, but you looked to be very occupied and I was there on official business; it would not have been gentlemanly to involve you. Besides, I am not sure I could have controlled my actions had we been in such close proximity. The things that I should like to do to you in that gown—though there far more things I should like to do to you out of that gown. Kissing every inch of your skin, for example. And perhaps my mouth might travel further downwards to places that are not discussed in public company…

I must stop myself now before I continue any further and make a mess of myself that I should be most embarrassed to explain to Matthew in the morning.

You have bewitched me,

T.

May 28, 1814

S,

Please forgive me. The content of my last letter was most ungentlemanly and I must beg your pardon for speaking in such a manner. I know we vowed to be honest with one another, but I forget sometimes that you are a lady and that I should endeavour to behave myself more properly in your presence. It will not happen again.

Your most humble servant,

T.

May 28, 1814

Darling,

Please don't be ashamed about the content of your letter! I know that it's likely considered ungentlemanly and my mother would certainly be horrified to read such a thing, but I must confess, I enjoyed reading it immensely. I have decided to keep it under my pillow so that I can read it when I am missing you and pretend that you are here with me doing all those most scandalous things you would like to do with your mouth. (I happen to quite like that mouth, in case you weren't already aware.)

I shall not accept your apologies, for there is nothing to be sorry for; in fact, it is I that must beg your pardon for taking so long to reply and causing all the confusion in the first place! The house has been absolutely filled with callers dropping in to give their opinions about Mary and Matthew's wedding, which, of course, Mary hates, and the servants hardly had any time to deliver the post, nor I any time to read it. By the time I received it, your second note had come in the post.

I do feel terrible for the confusion, but please do not hesitate from expressing any most ungentlemanly feelings you might have in future letters.

All my love,

S.

P.S. I think I might tell Edith about us. She is most trustworthy, and I can't bear keeping the secret to myself much longer. I would so love to have someone to lament to about my terrible loneliness when you are away, and I think she might understand me quite well.

Downton Abbey, 1815

"It is a truth universally acknowledged that a single man in possession of a good fortune must be in want of a wife."

Lady Sybil Crawley pauses for dramatic effect and glances over the top of her book, eagerly awaiting her audience's response. The result is very disappointing: her sister, Edith, nods vaguely, without looking up from whatever she's furiously scratching onto her stationary. Cousin Rose doesn't respond at all, nose still buried in the society pages of the Times. The only one who bothers to respond at all is Mary, who raises one eyebrow and says, "If there is a point to this, darling, do get on with it. We haven't all day to sit here and play at guessing what's in your mind."

Sybil bites the inside of her cheek to keep from groaning in frustration. She's just read aloud a piece of life changing literature, and no one seems to care—not even Edith, who's always had a vested interest in storytelling! "Do you not see?" she asks with as much patience as she can muster.

"See what?" Mary asks dryly. "That every man of wealth desires a wife? If this comes as a great shock to you, then you ought to be concerned—surely you know that all men in general desire to be wed."

"I hardly think that's the point, Mary," Edith quips without looking up from her work.

"Yes, exactly!" Sybil exclaims, relieved to have someone on her side. "Do you not see the irony?"

"What irony? If I'm not mistaken, darling, she marries him in the end."

(This is exactly why she never wants to talk about books with Mary. Anything involving politics or women's rights, really, is off the table—not because her sister is against them, exactly, but because arguing with Mary's barbed wit is like running headlong into a brick wall. Repeatedly.)

Sybil is saved from a very unladylike retort by the arrival of Anna with the afternoon post. Mary has a missive from Matthew that looks to be as long as her forearm, Rose has a note from one of her many friends in London, most likely, and Edith has what looks like a telegram from one of the various magazines that she writes for. Sybil's heart is suddenly pounding loudly against her ribcage and she tries not to hope too much for there to be a letter with her name on it—he is very busy after all, and it's quite dangerous for him to send her letters from France, though he insists on doing it all the same—if only so as to not be quite so disappointed when it doesn't come. He'll be home in a few weeks, but until then, she can wait.

"A letter for you, Lady Sybil."

Sybil's heart, galloping a mile a minute, nearly stops dead as Anna holds out the missive. It's nothing extraordinary: a piece of paper folded in half and sealed with a piece of candlvwax. Written in a hurry then.

"Thank you," she murmurs, hoping that her face doesn't convey the terrible anticipation she feels. She never knows what each letter will contain: good news, or the announcement of a terrible end? (The excitement is part of the attraction, to be sure, but really, she'd be just as happy if he were a chauffeur and their lives weren't unfolding like the plot in a novel.)

Mary and Rose are immersed in their own post, but Edith flashes Sybil a knowing smile over her telegram as she breaks the seal.

My love,

I haven't much time to write, so you must excuse the terrible appearance of this letter—I don't mean for it to appear quite so dishevelled, though it is written in great haste. I am returning to London ahead of schedule, perhaps to receive a new assignment (one can never be sure) or perhaps for a longer stay, but I know for certain that I shall be in the country for the holidays. Matthew, I believe has some business in Downton over the holidays, both of a personal and professional nature, so I have every excuse to accompany him, though I must confess my desires are of a far more intimate nature. I am eagerly awaiting our reunion—I should so like to hold you in my arms after months of dreaming of it.

Yours most ardently,

T.

Sybil struggles to control the smile tugging at the corner of her mouth. Christmas has always been her favourite time of year— the whole house is infused with holiday spirit from the massive fir tree in the entrance hall and garlands on the banisters to the mistletoe that Daisy and Gwen have a little too much joy hanging over all the doorways in the house—and she can think of no greater joy than sharing the holiday spirit with Tom. Her fingers itch to write a reply, half out of habit and half from the desire to express feelings towards him she cannot let show, only she knows he and Matthew already departed from London and the missive would not be received until well after Tom had departed for London again. She resolves to do the next best thing, and slips into the newly prepared guest room the as soon as word is received that the guests are on their way up from the station to deposit a folded slip of paper on the nightstand.

Dearest T,

You cannot imagine my surprise upon opening your last letter! Downton is a lovely place, especially at this time of year, and my delight at sharing its secrets with you is very profound. It has been far too long since we have last seen one another, and yet it is as if you never left—you occupy my thoughts constantly.

Yours,

S.

P.S. My bedroom is three doors down the hall. The servants should not be about after eleven.

They're delayed, of course, by the snow, so the family is already seated at dinner when Matthew and Tom arrive, cheeks ruddy from the cold, brushing snowflakes off their collars. The tip of Tom's nose is the colour of a candied cherry and Sybil has the most delightful urge to press her lips against it when he enters the dining room. (She can't, of course, but she wishes to desperately.) Mary makes a grand show of pretending to be most uninterested in Matthew's arrival—which is ridiculous because they're engaged—and Matthew does a very poor job of hiding his amusement. Granny goes on for far too long about the indecencies of the lower class and how fortunate Tom must feel to have escape the unfortunate circumstances of his birth (one of seven children whose father was a chauffeur in Ireland). Sybil is mortified on Tom's behalf—she happens to know he is terribly proud of his heritage and is a great advocate for the lower class in London—but Tom simply smiles and tells Granny quite sweetly that there are many members of Parliament whose circumstances are for more unfortunate than his. There's a ripple of polite laughter around the table, but Sybil can sense her family's unease.

(She overhears Granny telling Edith that it's such shame Matthew's aid is a socialist when they retire to the sitting room afterwards.)

A courtship with Tom is hardly be easy, Sybil reflects as Gwen helps her undress, frustrated that she and Tom had no time to share more than a glance with one another across the table throughout the course of the whole afternoon. He is the antithesis of everything her family desires for her, and a match with him would certainly ruin her reputation.

And yet, Sybil can't deny the rightness of the situation. She met many young men in her first season, all of whom were eligible and very acceptable, and yet, none of them can hold a candle to Tom. He treats her as his equal and encourages her to follow her passions, which is more than can be said for the men of the ton, Tom Bellasis included.

She is leaning over to blow out the candle, wondering if Tom would consider it too forward of her to knock on his door when she notices the slip of paper tucked under her much-loved copy of Pride and Prejudice. It bears no address but the handwriting inside is very familiar:

Meet me behind the Christmas tree in the foyer at eleven o'clock. I will be waiting.

T.

P.S. As thrilling as I find your postscript, I hardly think your parents will approve of my visiting your chambers after hours—or at any time. I must confess I am sorely tempted, but we must resist the temptation if we are to have any hope of one day gaining your parents' approval.

Her hands are trembling with excitement as she sneaks along to corridor and slips down the stairs. Her whole body is humming with a frightful energy. What she's about to do is terribly scandalous, and she'll be in ever so much trouble if she's caught, but she cannot bring herself to care.

Tom hovers in front of the Christmas tree, looking equal parts excited and terrified. He is still dressed for dinner, though he is no longer wearing his cravat, and Sybil suddenly feels exposed in her dressing gown. She turns, of half a mind to creep back to her chamber and put on a gown before she's seen. The stairs, however, creak terribly underfoot, and a simple uncertain shift of weight is more than enough to give her position away. Tom starts terribly at the sound, but relaxes when he sees Sybil. The smile on his face makes her heart feel as though it might burst out of her chest. She loves this man, really and truly, and there is no sense in denying it, class be damned.

"For a spy, you frighten awful easily," Sybil teases.

Tom grins, clasping her hands between his. "I can assure you, your father is much more terrifying than anything I might facet the hands of the French."

"He's really not that bad, for all his talk. I think he quite likes you."

"Liking me and approving of me as a match for his daughter are two very different things, m'lady."

Sybil sighs, cupping Tom's cheek with her hand. They've exchanged touches like this before, but her hands have always been gloved; it's quite another thing altogether to feel his bare skin against hers. Tom closes his eyes and leans reflexively into her touch. To think that she might have such an effect on another person, a man no less, is surprising but also terribly exhilarating.

"I really do think he might come around," she says softly. "He doesn't want scandal of course, but I truly believe he doesn't want his daughters to be miserable, either. He's not so obsessed with his own wealth that he can't be made to see reason."

Tom's answering smile is small and rueful. "We shall remain hopeful then. In the mean time, however, there's something I must ask you."

Sybil swallows. Her heart is pounding frightfully loudly and she wonders vaguely if Tom can hear it. She has read more than enough novels to know what is coming next.

"I'll speak to your father and ask for his consent properly in the morning—" Tom breaks off, dragging a hand through his hair. "I know it's terribly ungentlemanly of me, but I cannot wait any longer. Will you do me the great honour of being my wife?"

She wonders if this feeling, this wonderful elation that makes it feel as though every nerve in her body has been set aflame, is what novel heroines mean when they say that they feel as though they might die of happiness. She doesn't think it will kill her—it's far too pleasant—but it does feel as though she's been connected from her body, or at least her rational mind, and if she were to die here right now, it would be a deliriously happy death.

"Sybil?" Tom frowns, squeezing her hands between his. There is the smallest flash of panic in his eyes, which she can tell he is trying to conceal. Sybil wonders why he might be looking like that, why he isn't celebrating when their lives have changed in such wonderful way, until it occurs to her that she hasn't made any reply.

"Oh, of course!" she exclaims, cheeks flushing. There are tears in her eyes, though she's not sure if they are from joy or nervousness or embarrassment. "Yes. Yes. Nothing could make me happier."

The very first thought that flies through her mind when Tom kisses her is that they really should be doing this somewhere public where they might be seen, but that evaporates very quickly when Tom's tongue starts doing very delicious things to the inside of her mouth and she can't bring herself to care about anything.

It isn't the first time they've kissed (that was last Christmas in London, right after Matthew proposed to Mary), but it feels different somehow. Perhaps it's the excitement of being newly engaged to the love of her life (and secretly at that), or perhaps she's been reading too many novels, but this moment right here, kissing Tom with everything she has underneath the Christmas tree, is possibly the most perfectly beautiful moment of her entire life…

"Sybil?"

They spring apart. Tom is staring at something above her head in horror. Sybil can feel the blush flaming across her cheeks as she turns around.

It's Rose, clad in her dressing gown and leaning against the stair rail with an expression of delight on her face.

"Rose—" Sybil is laughing now, helplessly, as Tom looks on with a mixture of confusion and humiliation. Sybil would reassure him that everything is perfectly all right, if she weren't so relieved that it is Rose of all people who's come across them. "You gave me the fright of my life!"

"I should say the same about you," Rose says with a saucy grin. "Sneaking around the corridors at night and kissing gentlemen in the middle of the hall when you're not yet promised—whatever would Granny have to say about that!"

"We are promised actually." Tom seems to have recovered his senses, if the smile spreading across his face is any indication. Sybil can't help feeling giddy herself.

Rose, of course, is delighted and insists they sneak down to the kitchens for some celebratory champagne. They drink it in teacups at the kitchen table, while Sybil and Tom tell Rose the whole story of their courtship, and Rose tells them how very unsurprised she is. ("Edith and I have known for ages; honestly, Sybil, how else do you think it is that no one found out about you slipping out of the house at all hours?")

They stagger back to their rooms an hour later, pleasantly warm and unfathomably giddy. Rose trips up the stairs with a knowing wink and Tom kisses Sybil again under the Christmas tree.

She's not sure she can remember a better holiday.