John slows to a stop and looks back at the trail of their footprints down the beach together, side by side, warm and happy to have Sherlock here with him. He sighs. "Do you ever look back at your life like this? You know, see it laid out behind you like footprints in the sand?"

Sherlock casts a disparaging look backwards. "Why would I? Footprints in the sand only last until the tide comes in, and then they get washed away and forgotten about." He's picked up a piece of driftwood along the way, and is holding it out in front of him like a wizard with a staff. John snorts, then frowns.

"Not us, Gandalf. You, at least, people will remember."

Grey eyes turn on him, Sherlock's caterpillar eyebrows contracted above them. "It's not fair," he says softly. "It should be you. Your footprint trail is far more impressive than mine."

"How so?" John asks, surprised. He's never seen it like that; Sherlock's very existence is a blaze of glory and energy and intelligence, and his own… well, it's his. He's never looked at it as impressive before.

Sherlock hitches the staff up in his hands and walks a few metres back down the beach. "Here," he begins, drawing a line across John's footprint path. "You were born. You had a childhood full of love. Your parents loved you and cared about you. You and Harry hated each other, but it was fun to hate her, and even though you were scared of her sometimes you still knew that if it was serious, she'd support you." He draws a line beside the next footprint, shooting upwards like a tree-branch. "You had a good time at school. Well-liked, good grades. Head boy in your last year of college. Then you joined the military." Another line, rocketing up towards where John still stands. "You joined because they'd pay your way through medical school, didn't think you'd actually be called to serve, but you didn't think you'd mind if you were; you're strong, and you love adventure and excitement. You completed your doctorate with good grades and got a job as a surgeon, where you saved lives every day. Hundreds of people are indebted to you, are alive because of you. Already, John, you'd made a mark."

The first two-thirds of Sherlock's makeshift timeline look like a demented deciduous tree in winter. It doesn't look too glorious to John; he remembers the things Sherlock's talking about, and none of them were anything like as noble as Sherlock seems to be trying to convey.

"Then you get called to Afghanistan," Sherlock continues, his voice softening, losing its excited quality as he looks up at John again. "There's sacrifice, and pain. You see things, lose things, that you never wanted to. There are horrible things." The line this time goes right through the footprints, and John understands: this is another chapter of life. This is where he grew up, finally. "But you're a doctor. You're strong, and brave, and selfless. People die, but some people don't because you save them. John, you've done such amazing things. How many people out there are alive because you saved them? You have no idea, because there are so many. I could never have the strength to do that."

The consulting detective draws in a shaky breath as though he'd got sidetracked, and draws another line through the timeline. "Then you get shot," he says matter-of-factly. "That's not nice, and it hurts like hell, but really it's lucky for you, isn't it? It could have been a lot worse. And then you get sent home. You meet me, move in with me. You like it here; it's exciting, it sates your thirst for excitement and adrenaline. And you're still saving people. You've saved me more than once."

Sherlock stills, walking the last few steps to join him again. "Your life, John," he says quietly. "It's been worth something."

John frowns, trying to repress the unbelievably strong urge to hold and squeeze. "So has yours," he protests. The detective makes a face.

"Mine?" he repeats briskly, stalking back to the beginning of John's line, this time focussing on his own footprints. He draws an identical line. "I was born. It was an accident, and my parents regretted it straight away. Mycroft was the perfect one, they didn't need me – I was the unruly child that drew on the walls and blew up the stove in the kitchen. Mycroft and I hated each other, too, but it wasn't like you and Harry; he would have sold my soul if it helped him, especially when he decided he wanted to go into politics." He stills briefly, then draws the first sharp, spiky branch. "Then when I was eleven, he left home, leaving me to the mercy of my father. Sure, Mycroft and I hated each other, but we always tried to help each other to avoid my father because we wanted help ourselves. After Mycroft left there was no-one to stop him. Mother didn't care. He taught me the violin, and every time I played a note wrong or fumbled a vibrato he beat me until I got it right. When I was fifteen, I ran away."

Another line scratches into the sand with bitter vehemence. Sherlock's face is emotionless, intent on its task. John wants to reach out and comfort him; he knew Sherlock's childhood was bad, but he never wanted to ask. "Mycroft grudgingly lent me money to rent a flat, because he knew Mother would be upset if I died on the street. The flat was awful. It smelt of urine and the other people in the building were people I never wanted to be like. But it was hard to live in a place like that and not be corrupted a little bit; I started shooting cocaine and chain-smoking." Sherlock savagely stabs out another line in the sand. "From there it's boring. Drugs, depression, hopelessness."

Sherlock breathes in and draws a thick line across his foot-path. New chapter. "And then someone was murdered in the old building I bought cocaine from and Lestrade turned up to investigate. They were doing it wrong. I told them, and Lestrade arrested me for cocaine possession." He sighs. More lines stretch towards John as though he is the sun, the food, the life-blood. He starts to feel uneasy. "Mycroft bailed me out. He was furious, but only because Mother was distraught. I always thought it was funny –she'd never cared about me before. I went to Lestrade to help me through withdrawal because I didn't have anyone else, and he gave me enough help to set up my business. Started calling me to help him instead of glaring at me when I turned up uninvited.

"Then my business started doing better. I met Mrs Hudson. She… cared. I hardly knew her, and she force-fed me homemade muffins until I threw up and collapsed on her sofa." Sherlock's face has dropped its carefully closed expression in favour of a warm smile. "We came back to London together. I was carefully building myself a proper family, a proper life. But it was still… boring. Mundane. I still craved the cocaine, sometimes, just for something to do. I met Molly, and then experimenting became a thousand times easier and more profitable."

This last line in the sand has brought him all the way to the end of the footprints. John thinks he'll carry on, keep walking to create more. Instead, Sherlock draws a long, final-looking line at the end of the footprints and pauses, looking at it. "Then I met you."

John waits a long time for him to elaborate, but after a few minutes that stretch out like years, he drops the stick in the sand and walks away.

He doesn't make it very far before he stops, looking back and frowning at John, wondering why he isn't following. John's still staring after him, nonplussed. "And then what?" John asks, scrambling to catch up. "And then you met me what?"

Sherlock blinks. "And then I met you, and… I don't know what else you want me to say, John." He sounds confused, as though the answer should be obvious. John recognises the Face that accompanies the Voice and tries not to get annoyed. "Then I met you, and my life stopped being a simple progression of events. Then I met you, and my life… exploded. Then I met you, and I had better things to do than quantify my life as a series of footprints and lines in the sand."

John tries to swallow, but suddenly finds it just as hard as the detective seems to be finding the next few words he wants to say. "I… I know I don't show it, John, but I do care for you."

He's not quite sure what his heart is doing right now, actually it feels like his heart hasn't quite made that decision yet either; does it want to melt or jump into his throat and attack his uvula? He tries swallowing again, with little success. "I know that," he says firmly, trying to keep his voice from shaking. "Of course I know that – you don't have to say it, or buy chocolates or thank-you cards for me to know you care. It's just who you are, and I know you well enough by now to understand how you say thank you and I care about you." Sherlock smiles half-heartedly, so John claps him violently on the back. "And I think you're forgetting things in your little life-line there, Sherlock," he admonishes, turning back to it. "What about all the lives you've saved? Angelo. Mrs Hudson – she told me about her husband's plans to kill her. Sarah. Those people Moriarty strapped to bombs. Irene Adler – yes, I know about that. Henry Knight. Doctor Mortimer. That banker. Me, and me, and me, over and over again – I owe my life to you a thousand times, Sherlock."

"You're exaggerating."

"A little bit. But that's not the point."

Sherlock gives him one of those rare, indulgent smiles, the ones he's never seen him give anyone else. They walk on in silence until they reach the ridge over which the crime-scene can still be seen; John stares down at it, watching Hutchinson direct people around wearing white body-suits and looking like sperm in some kind of television advert.

"Funny thing, isn't it?" Sherlock says suddenly, his gaze directed resolutely out to sea.

"Hmm?"

The detective casts a quick glance back at him before redirecting his eyes back to where they came from. "Love." He says the word without emotion; no trace of disgust or ridicule, but none of reverence or even acceptance either. "It makes people do such awful things."

John suddenly wonders if there was someone, once, some cold older man or woman who broke a young Sherlock's heart. "Have you ever done it before?" he asks.

The consulting detective turns his head to stare at John in an absent manner. "No," he says finally. "I've seen what it does, why would anyone willingly subject themselves to that?" John takes the moment to marvel in the things Sherlock doesn't know. "I imagine it hurts."

It makes a stab of sadness catch at John's heart that Sherlock really has no idea. "Sometimes," he agrees. "But most of the time it feels like…" he pauses to consider, to give Sherlock the most honest approximation. "It's what I always imagined flying would feel like. It's exciting, there's adrenaline, and it's… it makes you feel alive."

There is silence for a few moments as the consultant considers this. "How many times have you been in love, John?"

The doctor replies instantly. "Three. Although, the first one was when I was a teenager, so I'm not really sure it counts." Sherlock doesn't say anything to this, and so John finds himself staring out at the sea and thinking how perfect this is, him and Sherlock on a beach, barefoot with their shoes dangling from their fingers, loose and totally comfortable with each other. He recognises that it's clichéd, but he cannot think of any other place in the world he would rather be.

"I've had fun," he muses aloud. "I have actually enjoyed myself, here in bloody Brighton." He slows down, steeling himself for what he suddenly knows he's about to do. Sherlock stops too. John turns to look at him, and the detective smiles lazily back. "Here in Brighton, with you."

He breathes deeply, then leans forward on tip-toe until he can see the blush rise on Sherlock's cheek, see the rapid fluttering of the pulse-point on his neck galloping in time with John's own. Elevated heart-rate. Quickened breathing. Flushed face. John figuratively shakes himself, takes the plunge, and presses his lips to Sherlock's.

The lanky detective stutters in fright and steps back, breaking the contact abruptly. "John!"

John opens his eyes, breathing hard, suddenly feeling ill. This isn't how that was supposed to go. "Did I do something wrong?" he asks carefully. Sherlock's eyes are wide with something akin to terror, but his pupils are blown and he raises a pale hand to touch his lips as he stumbles a few more steps back.

"John, I don't… I didn't… I don't want…" Were it any other situation, John would be proud of managing to bring Sherlock to this level of incoherence, but right now he feels like someone just pulled a rug out from under his feet. Sherlock had wanted him to kiss him, he could see it – all of the detective's own identifiers were there. "I, um… I'm flattered that you want me like that, John, really," Sherlock finishes quickly. "But I don't feel the same. I'm sorry."

"Yes, you do," John affirms quietly. Sherlock stops in his tracks and stares. "Did you think I hadn't noticed? I'm not stupid. Your pulse is elevated, you're breathing faster, you're going red, and your pupils are dilated." John tries to take a step forward, but Sherlock steps back, holding the distance between them, looking horrified. "Sherlock, please," he says desperately. "It's all right, I won't let you go. You trust me, don't you? What's the worst that could happen?"

Sherlock meets his eyes for a moment, and in them John sees fear and something pure, childish and naïve. Then the detective clears his throat and breaks the contact. "You're mistaken, John," he says shortly. "I don't want to pursue that kind of relationship with you, and I'd appreciate it if you respected that wish and maintained a reasonable distance between us. Our train leaves in an hour, we should get back to the hotel."

And he shrugs his shoulders a bit, awkwardly, and starts back towards the road.