John's newest girlfriend is taller than him, with pale skin and wild dark hair, and I'm finding it difficult to continue to ignore the data that's being constantly thrust upon me. He brings her home one night (I've deleted her name- Lisa? Lina? Louie?) and I eye her, noting the boring receptionist job that makes itself evident in her fingernails, the two cats (one male and ginger, one female tabby), the cigarette habit she is failing to kick (and which John is politely pretending not to know about), and the bland quality of her banter with something like loathing. I'm glad when he finally whisks her away to his bedroom, and I wait a careful three minutes, forty-five seconds before ascending the stairs myself (avoiding the creaky fourteenth step with practiced ease).

I still my breath and press my ear to the door. It isn't much, but from the small rustles of fabric and occasional gasps I can work out the scene in my mind with relative accuracy. They're "snogging", as John likes to term it, with the girl on her back and John above her. I can hear the exact moment he slips his hand up her ugly secondhand skirt. Their activity suddenly takes on a frenetic quality; clothes hit the ground rapidly, the bed squeaks with their movement, the gasping increases.

"Turn over," John growls, and I'm surprised to find myself reacting physically. I'm aware that my interests in John extend beyond those of platonic friendship, but simple lust has always seemed so banal, so exceedingly carnal and dull, that I'm intrigued to discover I'm enjoying the feeling. I can hear the girl sit up, go to her knees. This isn't how I pictured John engaging in sexual activity (the fact that I have pictured John in such a situation bothers me immensely) and I spin this new piece of data around in my head for a moment. In my mind, John is a tender lover, gentle, with a preference for the missionary position and a great deal of "foreplay". The John of reality seems much more gruff and hasty, then, by comparison. I don't spend long on this line of thinking, though, because I'm drawn back by the noises John is making. I know almost everything about John, and I know that when he watches pornography and masturbates he is near silent, only huffing the occasional breath from between gritted teeth (a habit I suspect he has brought home with him from Afghanistan, but one that he undoubtedly picked up, initially, at uni). Ignoring the slap of flesh on flesh and the obscene, throaty noises of the girl, I can hear John panting, gasping, letting out a rare moan and a very infrequent, hushed, "Yes."

"Fuck," John says, and the movement comes to an abrupt stop. Obvious: rapid, repetitive movement is hard to sustain; I imagine he's slipped out. I expect the pace to resume immediately, but instead the pause grows and suddenly John suggests, in a rather sly tone, "Might we try that thing this time round?"

It doesn't take much to deduce that this isn't the first time John's suggested "that thing" mid-coitus; the noise the girl (I say girl, of course, but it's hardly a fair description of this woman: thirty-seven years old; lives in a decent flat that she claims as her own but which, in reality, belongs to her mum; two failed engagements and she's trying to tell herself that John is The One when all three of us are aware that he clearly is not) makes in response is both is both amused and annoyed. "You can't be talked down, can you?" she asks, breathless.

John's laugh sends a strange shiver down the length of my spine. "Ex-army, love." I can hear him give her rump a little slap, and my face goes warm. "Once I've got a target in my sights…"

"Mm-hmm." The bed creaks; she's turning over. "I told you, my ex at uni put me off from it. I mean, John: it hurt like you can't imagine."

My eyebrow lifts. What is he suggesting? A more thorough spanking? (I'm not blushing; it's warmer up here. Simple science.) John has a smile in his voice as he murmurs, "Ah, but I'm a doctor. Surely I'll be more gentle than some sodding schoolboy?"

Laura/Louise/Lana sighs. "Well…it's kind of dirty, too, innit? I mean…you know…"

"No dirtier than anything else, really." I like John's tone; it reminds me of the one he uses when he wants me to eat, or sleep, or tidy the flat. "Sex is sex, right?"

"Hmph."

"We don't have to," John says, not quite resigned.

"Maybe another time, baby? I just…I really need to think about it." I can tell from her tone that she's done discussing the matter (which I've decided must be anal sex, though I don't understand why heterosexual couples partake in the act when there's a perfectly serviceable hole just above- or below, I suppose, depending on the position- the one in question) and apparently John knows she's not budging because he drops the issue, instead doing something that makes her laugh loudly.

"Get back on your knees, miss," John barks, but he's using his playful voice. "Hop to it."

"Been at work all day, pet," the girls sighs. "Can't we do it lazy-like? I'll just lie back and…" Something in his expression must give her pause, because she says, with the faintest hint of frustration, "What? C'mon, I'm well spent here! It's not like we're teenagers, mm? Give a girl a rest."

John yawns, which does not seem at all congruous with sexual excitement. "Right. Well. If you're spent, we could call it a night." It's obvious that he's only suggesting this out of politeness, but the girl sighs again and mumbles, "Yes, that could be nice. Mind if I kip here?"

"No, that's…fine. Fine." The bed groans; the sound of the weight coming off it makes me think John must have just stood. And…yes, I can hear him pacing over to get his dressing gown from the hook on the door. We're only inches apart, now, and I know I should dash downstairs, but something compels me to stay. "You go ahead and catch some sleep. I've got some work left to do for Sherlock-"

At my name, the girl laughs without a trace of joy. "Of course! Of course you do. Never mind that it's my night, never mind that I have to claim a night and even still you sometimes run off on cases-"

"Don't start that again." John steps away from the door. "We've had this conversation. I thought you understood how important the work is to me."

The work. Even the girl realizes how feeble that sounds, because she laughs again and says, her voice a little shrill, "I know there's something damn bloody important to you, and I don't think it's the bleeding work."

"Just what are you getting at?" I like this tone, too; it's John's back off voice. I've noticed that it only ever comes out when I'm involved and he feels I need protecting.

"You know exactly what I'm getting at," she snips, and I can hear her getting out of bed. "I can't deal with this, John. I can't…" She's getting dressed rapidly. "Call me when you're actually single, okay? Because I know perfectly well that I can't compare with Sherlock bleeding Holmes."

The door pushes open so suddenly that I'm almost struck by it. I hunch up in the corner behind it, willing my breath into absolute silence, as John pads out on to the landing (the girl already pounding down the steps, trainers untied- I can hear the click of her laces as she goes) and calls, "Lucy? I…" The door to the flat slams with a vibrating ring, and John sags his weight against the door, sighing. "Christ." I'm trapped in the triangle of space between the door and the corner of the landing as John leans on the door, his breathing slow and deep. Eventually he says, rather sharply, "No. No way, John Watson; that is a terrible idea." I want desperately to ask him what his terrible idea is, but before I can debate the merits of him getting stroppy over me eavesdropping he lifts up from the door and yanks it closed behind him, the sudden darkness of the landing making me blink.

I stare at the door for a long moment, the words still lingering on my lips: What is your terrible idea, John? What is it? But I already know. When the impossible is eliminated, whatever remains- however improbable- must be the truth. It's improbable that John has romantic feelings for me.

But it isn't impossible.