You wonder, as they come in late, and think you haven't seen them kissing in the corridor, how long they're going to try to keep their relationship a secret from everyone, even though Charlie's already given you a knowing grin, and it's only just gone nine. You pretend not to notice, and wonder how long you, too, can keep up the pretence that nothing's changed.

You feign surprise two weeks later when you walk in on them kissing in the locker room, and pretend to be annoyed with them for keeping you in the dark (when, actually, you're really rather amused by the whole thing).

You smile when you see them at the office Christmas party, kissing under the mistletoe. Everyone knows, by now, but that doesn't stop Charlie from giving an audible 'Awwww…' (you suspect she's probably had a drop too much mulled wine), and Janet from nudging you in the ribs and grinning broadly, nodding in their direction. You're relieved they've gone public; it'll stop all the lab techs going weak at the knees over Harry, and the whole of the London Metropolitan police force from testosterone-fuelled masculine posturings around Nikki. Well, you hope so, anyway. It was all getting a bit much.

It rather amuses you that there'll be so many broken hearts over the pair of them, and you wonder when you turned into a grumpy old man. Then Janet smiles lovingly at you, and you realise that you're neither grumpy nor old, you're just acknowledging that these two young colleagues of yours are meant to be.

You're delighted when Nikki comes in one day in mid-February, when they're back from a long weekend in Paris, and proudly shows you the white-gold Cartier ring, set with a dainty diamond solitaire, that graces her finger, and tells you in an awed whisper that Harry proposed at the top of the Eiffel Tower as the clock struck midnight on Valentine's Day, and it was so romantic, with all the lights twinkling all over the tower, and the stars in the frosty sky, and the view over the Seine, and Harry down on one knee… and despite it being horrendously busy, because they've been away for a couple of days and there's been a spate of murders, and there are bodies piling up in the morgue, you still sit and listen, wrapt, because it sounds like something from a fairy-tale.

You get a bit emotional when you walk Nikki up the aisle, because she said she'd rather you gave her away than her own father, and because you never got the chance to walk Cassie up the aisle, and never will. But then you smile, thinking that Janet didn't want to know if she was expecting a girl or a boy, so you might still be able to walk your daughter up the aisle one day, as well as Nikki.

You look on proudly as they say their vows, submit to the endless photographs, and get so nervous about the father of the bride's speech that you very nearly fluff your well-rehearsed lines, and it's only Janet, sitting beside you and smiling, that calms you down enough to get through it.

You wave them off on honeymoon, and groan, thinking how long three weeks without them is going to be, and wonder whatever possessed you to sign them off for that long. Then you remember Nikki's beseeching look when she told you that Harry wanted to take her back to South Africa on honeymoon, and you couldn't resist that look, any more than you could when she first gate-crashed your mortuary. You groan again, thinking how quiet it's going to be without them.

You wonder if they'll send you a postcard.

You grin proudly at them when they come to see baby Nicola Jane, and hand Nikki a tissue when she realises you've gone and named your daughter after her. You hand her another tissue as you ask her if she'll be little Nicola's godmother.

You cry tears of anguish when she miscarries her first child, a little girl, and tears of joy when she gives birth to baby Leo Harry, and tears of delight when you realise she's gone and named her son after you.

You listen when she pours out to you her confusion over her desire to work and her need to be a good parent, and you discuss all the options with her, not knowing whether you're hoping she'll follow her heart or her head. You feel torn when she works part time for a while, while little Leo is still too little to be left overmuch, and breathe a sigh of relief when he starts at nursery, and she comes back to work full-time.

You cry openly when she names her twin daughters Theresa and Cassandra, and hug both her and Harry as though you never want to let them go.

You get a locum in, this time, because you and Harry just can't cope without a third person, and in any case, Harry's wrapped up in his new baby daughters and you feel bad about asking him to work late when he has two tiny ones to look after (because Tessa and Cassie are still remarkably little, and so cute...), as well as Nikki and little Leo (who's growing alarmingly fast; you suspect he takes after his dad).

You wonder why you asked the entire Cunningham tribe over to meet little Sam when he and Janet come home from the hospital, though you wouldn't really have missed seeing them for the world – even the two twin Cunninghams, at just three months.

When Nikki tells you she's expecting her fourth child, you threaten to take Harry to get him snipped.

When she's expecting her fifth, you seriously consider actually doing it.

When she very nervously tells you she's expecting her sixth, you think you'll actually do it yourself, until she bursts out into hysterical giggles, and you realise with relief that she's joking.

You put up with children running round the office, and even install a low table and a couple of small chairs so they can do their colouring-in under your watchful eye while their parents are otherwise engaged in cutting up bodies and talking to relatives of the deceased.

You boggle when, at the age of five, a precocious Cassie informs Janet that she wants to be a pathologist like mummy and daddy and Uncle Leo.

You're somehow unsurprised that little Leo wants to fulfil his father's ambition of being a pilot, and are unaccountably glad that he won't be prevented by a heart murmur. But you're still glad that Harry was.

You love the fact that your three children get on so well with Harry and Nikki's five, and you wonder idly if there'll be any romances there.

You get your answer when they all hit their teens, and all hell breaks loose.

You wonder why you ever thought having children was a good idea in the first place.

You smile proudly as Mia, a veritable mini-Nikki, the youngest Cunningham, marries James, your youngest.

You tear your hair out over Sam, who can't get over Tessa, who's head over heels in love with Tim, one of their friends, who's head over heels in love with Cassie, who's head over heels in love with Sam.

You feel for Nikki and Harry when Katie, the youngest-but-one, decides to go and work in a Kibbutz for a couple of years, and have a quiet chuckle to yourself when she's home in under three months.

You tear your hair out over Sam, who's head over heels in love with Katie, who's really just interested in vet school.

You walk Nicola down the aisle, and give a soft sigh as Janet gives you an understanding look and a hug.

You tear your hair out over Sam, who can't get over Tessa (again), who's still in love with Tim.

You cheer as Katie gets through vet school with flying colours, and announces she's got a boyfriend (who reminds you a lot of Harry when he was younger).

You tear your hair out over Sam, who's breaking his heart over Katie and her new boyfriend.

You're prepared to sit up all night with Sam when Tessa finally marries Tim, but he seems remarkably chilled out about it. The next thing you know, which defeats you utterly, is that he's telling you he wants to settle down with Cassie, who, thankfully, feels the same way.

It's become such a force of habit, you tear your hair out over him anyway.

You wonder why you ever thought that Harry and Nikki getting together would make life easier – but you know you wouldn't have changed it for the world.