"So what do you think you'll settle as?" John Watson sat cross legged at the end of his bed, watching a ferret-shaped Leofas wriggle around the covers as they had the conversation every child has a thousand times; the one without an answer.

"I told you, I don't know!" She replied indignantly.

"But you must have some idea..." John pleaded.

"I. Don't! You. Know. That. " She shifted on every pause for emphasis. John groaned and flopped onto his pillow. They were almost fourteen; half their class had settled. Wasn't it their turn? Even Robert Ferguson, the smallest kid in their school, had his daemon settled (in the form of a particularly twitchy possum). He just wanted to know already!

"What about when. You must know when it happens." He implored.

"John! I know as much as you do."

"Leo... you're not very helpful."

She rolled her huge owl eyes dramatically before turning into a warm, fluffy cat to nestle into bed with him. John roughly kicked his covers into place.

"How will we know when it happens?" John whispered, clicking off his lamp. "Will you just try and change and it won't work?"

"I think we'll know," his daemon whispered back in the darkness. "I mean, we won't know what I'm going to be until I am it. And then we'll realise it could never have been anything else."

The thing about daemons, thought John Watson as he limped stoically through London, was that they were inherently narcissistic. Your daemon IS you. Of course – of course he loved Leofas, and couldn't imagine for an instant life without her, nor did he wish it. But people needed to realise that the crushing loneliness that an Afghani bullet injected into his life wasn't curable by his daemon.

He wasn't alone. But they were.

Leofas walked beside him, left foreleg lifting slightly higher than the others on each step, ever-watchful eyes sizing up the menagerie of daemons passing them on their daily commute. John and Leo wandered without purpose, heading vaguely towards to the Criterion Bar, though neither of them had agreed on a destination. The pressures of a meagre army pension were weighing down their spirit.

"John – John Watson!"

And there was Stanford, and Talany, and wolf and badger greeted each other, and suddenly John's accommodation issues might not be issues any more.

Despite the years gone by, the hospital was still familiar ground to John, and they required no guidance by Stanford. Favouring the lift over the bleak stone staircase, John and Leofas were soon re-tracing old footsteps down the long, whitewashed corridors and into a chemistry lab.

John scoffed good-humouredly as they entered.

"Bit different from our day," he muttered to his daemon, nodding at the equipment filling the room.

"Mike, can I borrow your phone?" The only previous living inhabitant of the room asked without making eye contact, bending over a distant desk and absorbed in his work. As they spoke John glanced around for the man's daemon, and rather abruptly saw a proud, leggy cat; tan in colour with strong black markings. Her huge ears and blazing eyes were examining every inch of Leofas. Leaving the daemon to Leo, he offered the man his phone to use.

"An old friend of mine, John Watson," Stanford announced as the man strode over. John smiled before glancing back at the cat daemon, who hadn't moved a millimetre. The daemon's person flipped up the phone.

"Afghanistan or Iraq."

John paused.

"Sorry?"

"Which was it, Afghanistan or Iraq?"

"Afghanistan... sorry, how did you know?"

But the arrival of a med student drowned out his question, and suddenly his taste in violin music –but spoken into a laptop screen – was being requested. John and Leo barely had time to exchange exasperated confusion before being stunned into silence by a complete stranger reeling off a synopsis of their life story, informing them of the address and dramatically announcing himself to be Sherlock Holmes.

"Yep." Said Stanford. "He's always like that."

"So what do you think we should do?" John sat on his impeccably made bed, gazing eye-to-eye at his wolf-shaped soul.

Leo shrugged in a disconcertingly human way. "I'm pretty sure that was the most interesting five minutes we've had since the general anaesthetic wore off." She said, referring to the surgery on John's shoulder. John grinned sadly at her.

"That thing he did ... just ... listing our life. What was that?" He wondered.

"No idea," Leo supplied. "What was his name again?...Holmes?"

"Yeah. Sherlock Holmes."

She nosed his laptop. "Search it? Also I want to know what his daemon is, look that up too."

John's eyes rested briefly on his gun as he took out the computer. "...mmmm. Some kind of cat. What did you think of her?"

Leofas looked apprehensive. "She didn't move when he walked over? Not at all. Like she wasn't even concerned about the distance."

"It was a pretty short walk." John reasoned as the computer booted up.

"Yeah, but ...I dunno, it was weird!"

"What did she say to you?"

"Nothing."

John looked over, startled. "At all?"

"Not even when her person was talking to you, or even when she walked past to leave."

John frowned into the laptop screen as the wifi connected.

Generally daemons could be relied on to exhibit the true nature of two people's relationship, being far less socially constricted than their human counterparts. If their daemons didn't get on then the flat share wouldn't work out. And cat and dog daemons weren't generally compatible. Mind you, Mr Holmes hadn't seemed too concerned. Leo reared onto the table to see the screen better.

"Did she not like you?" He asked tentatively.

"No," she replied.

John pushed her muzzle playfully. "Can we not get cryptic here? This Sherlock Holmes guy is enough of an enigma as it is - "

Leo bit his hand softly as she always did in good nature. A wolf caress. He tried to free his hand but she hung on, tail wagging, forcing John to slowly type with one finger a description of Sherlock Holmes's daemon.

"Ok...loading now..."

"I think she was a cheetah," said Leo, releasing his hand.

"No, that's a cheetah there," John thumbed the screen. "Jaguar? No. She was too small."

They flicked through the photos when one seemed to jump out. John clicked it excitedly.

"A serval! What on earth's that?"

"Medium sized African cat..." they read together. The cats in the photos looked extraordinary, but daemons had a different, almost ethereal quality that made the images look like dull failures. Regardless of this, they had clearly discovered Holmes's daemon's settled form. Leofas stared at the screen.

"Her eyes were a sort of – steel-grey colour," she informed her person. John started typing in the search bar again. "You know, she didn't seem hostile. There was no fear, either. She just watched me – rather ferociously, but sort of like she was passing judgement on me? But she didn't react at all... was she accepting? Definitely not disdainful..."

"Leo. Stop rambling. Just tell me what you think in five words or less."

Leofas mulled over her thoughts before replying; "Supremely unconcerned."

John scoffed. "Well, I think we can see she why she's a cat. What on earth...?"

The page read - THE SCIENCE OF DEDUCTION.

Having retrieved his riding crop from the mortuary, Sherlock Holmes flagged down a taxi and opened the door for his daemon. She leapt in and gazed reproachfully at the driver's sparrow-daemon, ignoring its welcoming titter.

"You agree with me." Sherlock said to her once he'd directed the cabbie.

"Of course," Lavoisier replied, knowing he meant inviting John Watson to share their flat.

"A wolf daemon," He continued. "Your antithesis. Nevertheless - "

"She's not my antithesis." His daemon growled. "My antithesis would be a barnacle. The idea that canine and feline daemons don't get along is just foolish human sentiment."

"You observed her left paw."

"Of course," Lavoisier repeated. "I assume the phone explained the brother and the drinking habits?"

Sherlock nodded. "So? What did you pick up from his daemon?"

Lavoisier considered her observations. "Clearly a very good sense of smell, probably honed by medical and military training. She stood directly to the right of her person, as British military daemons do. Fur is permanently mattered in areas corresponding to military equipment straps. Despite it being winter at the moment, her fur is still in the summer coat phase, indicating a lengthy stay overseas in warm climate. Psychosomatic limp to mirror her person's. Overall, the daemon you'd expect – or even hope for – of an army doctor."

Sherlock smiled at her. "Or a flat-mate."

They rode in companionable silence the rest of the way to Baker Street.

Just two days ago, John Watson met Sherlock Holmes. Barely two hours ago, he'd killed a man for him. And approximately two minutes ago John Watson decided that was one of the better decisions he'd made.

They were polishing off the remains of a truly excellent Chinese dinner, during which neither had spoken much. John studied the man sitting opposite him.

"So ... your daemon is a ... serval?"

"Yes." Said Sherlock Holmes.

"Ok." John nodded.

No one said anything for a bit. A waiter cleared the table.

"So what does that mean, then?" John continued.

Sherlock frowned. "What does what mean?"

"That your daemon is a serval."

Sherlock gave a half-grin and leaned forward. "What do you think it means?"

"Uh ... okay, well. Servals are cats, which can mean a person is solitary and independent..."

"Good," Sherlock encouraged.

"Also quite...proud. Both in themselves and their appearance, cat-daemons tend to be quite ... clean..." John finished uncertainly.

"Very good!" Sherlock congratulated him. "So much for the general; we must focus on the particulars if we are to infer anything of use. Daemons are, after all, a physical embodiment and representation of a person's soul. So; what does my daemon say about me?"

John paused. "Do you want me to get all 'consulting detective' on you?"

"I want you to observe, instead of just seeing."

John threw his hands up in surrender. "And then you tell me I'm an idiot? No happening."

"No, John-"

John gestured to the restaurant. "Show me. I'll be the audience to your frail genius requires."

Sherlock seemed to consider objecting, but only for an instant. A smile broadened across his face. "Now ... daemons. Daemons can tell you everything."

John sat back to listen as Sherlock began his lecture.

"First and foremost is a daemon's form. Not just its settled form – a child's daemon can be particularly revealing; showing what it wants to be as opposed to what it must be. For example, an upset child with a bear-daemon is obviously at the opposing end of a spectrum to one with a mouse-daemon, even if they exhibit similar personality traits, such as shyness. Also, what a pre-pubescent person aspires their daemon to settle as also reveals much about them, and the great irony is that the harder they wish for it, the less likely it is that it will occur."

"I'm lost," John announced quickly. "How does wanting affect what your daemon will be?"

"You see the man on table two with the sheep-daemon? I can assure you that he desired a lion. A daemon associated with strength, power and nobility, which reveals a potentially crippling low self esteem and strong herd instinct. Therefore; a sheep. The daemon you want is invariably the daemon you won't get, because by lusting after that prestige you reveal your true nature; which is then personified upon your daemon settling."

Sherlock's own daemon suddenly leapt onto the table. "Sherlock, no man ever had a lion-daemon." She reprimanded him, the first sentence John had ever heard from her.

"No, of course. You are right." He replied, and she slipped down to sit on the chair next to him.

"Wait, what?" John was bewildered.

"Gender! Men have lionesses." Sherlock explained.

"Oh, right. Yeah. Why is that? That daemons aren't the same gender as you? I've heard of a case where someone was the same gender though, quite recently...In America..."

"Jury is still out on that one, I'm afraid." Sherlock drummed the table. "There's a correlation between it and homosexuality, but it isn't universal."

"Ah." John looked at the two halves of Sherlock Holmes sitting across from him.

"When I was a kid, all I wanted was for Leofas to be soft and cuddly." He thought out loud.

"Yes, a malformed pack instinct. Hence the wolf."

John said nothing, unsure if he'd been insulted or not.

A hideous scraping noise broke through the silence.

"Sorry!" Leofas huffed as she leapt onto the chair she'd pulled out next to her person. She was met with a blazing stare of disapproval from the serval-daemon, who'd yowled at the noise and attempted to cover her elephantine ears. "Sorry!" Leofas whispered to her.

"But even within a daemon's settled species there is a lot of room for variance, and hence deductions," Sherlock continued. "And of course the way a daemon relates to others is of paramount importance. A daemon is literally a glimpse into a person's soul, hence they are invaluable to me. Such a shame they vaporise upon death,"

Leofas looked affronted, but Sherlock took advantage of John's continued silence.

"You see the sheep-daemon? Sitting with a poodle-daemon. You see how their poses oppose; the poodle sitting and the sheep lying down. Not looking at each other but engaged in conversation. But – look! The waiter's daemon disrupts and immediately they both sit, even leaning towards each other. These daemons are in a long-term relationship."

"Ok... want to run me through that one?" John said.

"Twinning is the act of mirroring a person's actions. It happens when you feel attracted to or are in a positive relationship with that person. Body language and actions – such as drinking at the same time – included. Its most common form is when people walk in step with one another. But when two people are extremely used to one another's company, say after ten years of marriage, they begin to actively avoid twinning (well subconsciously) in order to assert their own individuality. But as soon as they are interrupted they immediately revert back to twinning, as it was their usual status for most of their relationship. Daemons will do it regardless of the physical similarity of their settled forms."

"Couldn't you just ... look for a wedding ring?" John asked weakly.

Sherlock motioned for the bill. "Not everyone is married, John."

As soon as 221B had been freed of police, Mrs Hudson had taken Sherlock's word that John would take the room upstairs to heart. Her excitement at showing him the room and its evidently newly washed, crisp linen meant John couldn't refuse her invitation of staying there that night. While she bustled around downstairs for a spare toothbrush, John ventured to ask Sherlock what had been on his mind since dinner.

"What did you want Lav..."

"Lavoisier,"

"What did you want Lavoisier to settle as?"

"I didn't," Sherlock replied.

"Huh?"

"I didn't want her to settle,"

John frowned. "Any particular reason? ...Or is that just a symptom of being a serval?"

"In my line of business it is sometimes practical to assume a disguise, a skill I have honed to the highest level." Sherlock explained. "I'm sure you can see the value of having a still shifting daemon. That's not to say she has an impractical settled form. Many times it was her sharp hearing and nocturnal vision that solved the case and convicted a felon – as I'm sure Leofas has assisted in your medical and military career."

"Yes, she-"

Mrs Hudson returned triumphant. "Now I'm off to bed, mind you boys behave yourselves. I don't want any violin at three AM, Sherlock." Her green woodpecker-daemon chirped farewell.

"I'm um, going to do the same," John motioned upstairs with the toothbrush.

Sherlock nodded.

"Night!" John called down a few seconds later.

"Goodnight, John." Sherlock said before following upstairs to retire to his own room. Leofas had left with John but she now crept onto the shared landing as he brushed his teeth, hoping to catch Lavoisier. The serval-daemon poked her head out of Sherlock's bedroom door a minute later.

"Hi," Leofas whispered.

Lavoisier sat down opposite her, both at the fringes of the comfortable distance from their humans. "Leofas-" The serval began.

"Leo," Leofas cut her off. "My friends call me Leo."

"Are we friends?" She looked startled.

"Well, we did kill someone for you today."

Lavoisier paused, then simply said, "Thank you."

Leo grinned wolfishly, gave the cat a big lick, and dashed away to John's new bedroom. Every night thereafter, without ever acknowledging it openly or admitting it to their people, the two daemons met in the hallway for a quiet chat.