You could have waited. Why couldn’t you wait?

The girl below me is writing a love letter. No, not a love letter. Definitely not that. The biro skitters across the note pad in jagged peaks and troughs as the train hurtles through the tunnel. You are tearing the heart out of me, she writes, with an impatient hand, then crosses it through savagely. More slowly she starts: I never thought it would end this way, the script more loopy and thoughtful this time but then it tails off, the pen zigzagging across the paper like the trace of a heart machine. Her roots need doing: I can see the pale brown line down her parting, fragile and vulnerable against the vivid chestnut. It’s maybe a bit too red, the chestnut: doesn’t do her skin any favours. Someone should tell her. There is a thin, almost imperceptible, scar at her hairline – a childhood injury perhaps. Or maybe this bastard she’s writing to did it. Maybe he swung a heavy fist at her one day, catching her a glancing blow on the head...

The train judders into Bank and people pour off. She doesn’t move as commuters push past, selfish and self-centred, banging one another unapologetically with their briefcases and their oversized rucksacks. She’s staring at the pad, her face bunched with - what? irritation? pain? I like the way she concentrates, pink tongue sticking out, as if there’s no-one else around. She hasn’t noticed me at all. The man next to her jumps up at the last minute with a muttered curse just as the doors are starting to close; his seat snaps up, catching her skirt. Stupid idiot. Without looking up, she tugs the fabric free, and starts rummaging in her bag. I’m just considering sitting beside her when some old woman, flesh leaking over the waistband of her skirt, pushes past me and thumps her fat arse down, giving me a challenging, faintly triumphant look . As if I care. I’ve got a better view standing up.

There’s a mess of tissues, receipts, tampons and lipsticks in the bag, which is a bit battered but good quality, anyone could see that. An old pen without a cap, a Blackberry, her Oyster card. I can’t see the name on the bottle of perfume but it’ll be expensive, that’s for sure. Everything about her is soft: the pale blue cardigan – cashmere, probably – the slithery skirt which falls around her thighs like water, her suede shoes with the spotted bows. Under her skimpy top, the swell of her breasts, smooth and unblemished, rising and falling with her breath. I try not to look down her cleavage, that’s rude, intrusive, but it’s hard to drag my eyes away. Why else would she wear something that low-cut? It would look tarty on someone else, but on her it’s romantic, voluptuous, inviting.

‘Sorry, love,’ croaks the fat cow beside her, with an apologetic laugh, as the train jerks to a halt at Borough and they are thrown together. The hulking great slob would crush her in a moment. I’d like to push her off her perch, see her sprawl on the floor of the carriage, all fifteen grotesque and disgusting stones of her. But the girl just looks up briefly, smiles and returns to her contemplation of the pad. ‘Blimmin’ rubbish, eh, these drivers?’ persists the woman, with a snort. ‘Think they’re Stirling Moss or summink.’ Can’t she see the girl doesn’t want to talk? Can’t she see she’s in a world of her own, that she’s hurting inside? I know how she feels.

It’s my stop and I ought to get off, but I can’t, not now. I know there’ll be trouble when I don’t pitch up, but I don’t care. There are things far more important than rules and regulations. At Elephant and Castle, the carriage empties some more. There are lots of spare seats now: it’ll look a bit odd if I stay standing, so I saunter over and take a seat a bit further towards the middle. I can keep an eye on her from here. Just then, she looks up from her writing, deep in thought, and, almost by accident, catches my eye. It’s only momentary – not more than a second, probably – but it’s long enough.

My heart jolts. As I look away, I smile to myself, but only inside. Don’t show your feelings, not at this stage. It’s like a game of poker, love. Doesn’t do to show your hand too early. The familiar fluttering starts in my chest and I slide my hand inside my shirt to massage my heart. They teach you that, to comfort yourself. Skin on skin. It feels good.

She’s packing her things away now – quick glance at the watch, flick of the eye up to the tube map. I’m guessing Kennington. Yes, she’s on her feet now, bag over one arm, the other holding on to the pole by the doors. She says ‘’Bye’ to the fat cow – I like that, even if the old woman doesn’t deserve it. Means she’s kind, considerate. Her legs are long and slender: you can see that under the thin skirt and her toe nails are pink and tiny. My mother used to say only whores painted their nails, but what did she know? She had no idea what beauty was.

I’m by the other door when she gets up and I follow her to the exit, the warm gritty wind blowing her skirt up in a kind of dance. She moves fast, lightly running up the escalator, so I struggle to keep up and I’m sweating by the time I get to the top, to see her slip through the gates and make for the street.

‘Guy!’ Her voice is high, but warm, with a hint of laughter coiled inside it. A man leaning on the wall, reading a newspaper, looks up and smiles. He folds the paper, pushes himself off the wall with one foot and strides over to her, towering above her despite her heels. Flower-like, her face opens to him as he bends to kiss her. I recoil, dipping back into the shadowy booking hall. I feel as if someone’s punched me. This can’t be the lover. Can’t be. Maybe it was only a peck on the cheek.

‘Am I late?’ I love her voice, teetering on the edge of a laugh, rich and creamy.

‘What do you think?’ he says, his voice deep and strong. ‘What was it this time? Overslept? Hungover?’

‘Signals failure at Old Street,’ she says, looking up at him with a smile, daring him to challenge her. I’m shocked. Why would she lie?

‘Yeah, right,’ he says dismissively, one hand in the small of her back as he propels her down the street. My mobile bleeps. I know who it is. He can wait. I set off after them, my armpits damp, still a little breathless. I feel the comforting bulk of my inhaler in my pocket. A woman bumps into me as she comes out of a shop, head buried in a bus timetable. I jab my elbow into her fat arm, then mutter ‘Sorry’ as I hurry on, almost running to keep up with them. It’s lucky there are lots of people about, because it might look a bit suspicious otherwise, me tailing them so close. I try to catch what they’re saying, but all I can hear are snatches of laughter and the odd phrase. ‘Not working for me … still don’t think it’s right … haven’t got the balance …’ I know she knows I’m behind her, but I don’t want him noticing – he’s a good six inches taller than me. But it’s not likely – not someone like him, so cocksure, so self-confident. He thinks he owns everything, thinks he owns her probably.

They round a corner and I almost cannon into them, stationary in front of me, facing each other. She sounds impatient. ‘Guy, for God’s sake, we’ve got to get them the next draft by Friday!’ I have to swivel past them, pretend I’m going further on, but as I pass them I look her straight in the eye and, yes, she knows it’s me. I’ve startled her – I didn’t mean to do that. Behind me, as I continue walking I hear him ask a question I can’t decipher then she says quite clearly, ‘No. Some bloke on the same train, I think.’ And then something I don’t catch. I keep moving, turning right into the next street so I can glance back at them. But they’ve gone. The road is empty.

My phone goes. This time, I answer it.

‘Colin?’

Well, who else would it be? It’s my phone, isn’t it?

‘You there, Colin?’

‘Yeah.’

‘Where the hell are you? You were due here half an hour ago. I warned you last time. You know the terms of your licence -'

I jab the off button.

Doubling back, I stroll casually past the doorway where I saw them last. Waterfall Productions, it says on a discreet brass plaque. The glass door is tinted; I peer in, catching sight of what look like film posters on the walls, just as the receptionist looks up, cold hard eyes in a hostile face. I know that look. She stares at me like I’m shit on her shoe. I’ve a good mind to throw the door open and –

The girl dances down the marble stairs, distracting the receptionist. ‘Coffee,’ she says, rolling her eyes. ‘His nibs must have his latte. Want anything?’

‘No ta, Lisa,’ says the other girl. ‘How’s it going anyway?’

‘Oh... you know. Two steps forward, three hundred back! We’re still re-writing the first scene. See you in a bit.’

And she sails out of the door before I have the chance to back away. There’s a moment, a moment when everything stops, the traffic, the noise, the breeze, everything. There’s just her and me, together, close, the two of us caught like in a photograph. Lisa. Lisa. Lisa. Her skin is perfect, flawless, her eyes a deep drowning brown. I see the colour flood her cheeks, her eyes widen, the muscles between them tighten. I want so much to smile, say something, but my mouth’s suddenly dry and the words are gone. Then her face changes, bunches, her lovely face contorts into an ugly mask and she falls back. ‘What do you want? Are you following me?’ she hisses. But I can’t answer. I shouldn’t need to answer. She knows.

She shoots a look back into the building, where the receptionist has got to her feet, and then suddenly she darts across the road. There’s a squeal of brakes, a shout and a stream of obscenities from the taxi driver, hanging out of his window. I dart into a nearby doorway as the receptionist runs out and Lisa raises a shaky hand in apology from the pavement outside the café.

‘You all right?’ calls the other woman.

Lisa just nods, looking up and down the street, as the taxi surges angrily away. I lean back further into the shadows.

‘What happened?’

Her voice when it comes is breathy, threaded with fear, ‘I dunno. Some weirdo. He’s gone now.’

As she disappears into the darkness of the café, I have to smile. Oh, that’s clever, Lisa, that’s really clever. Puts them right off the scent. That little break in your voice – very convincing. It’s the man, I guess, the tall bloke, her boss presumably. I suppose she has to keep him sweet if she wants to keep her job. Perhaps he’s watching out from an upstairs window, checking up on her. He looked the jealous type. We’ll have to be so careful.

She doesn’t see me when she crosses the road five minutes later, two coffees in her hands. This time she looks both ways before stepping out into the road. I stay well back. There’s no point rushing these things. I’ve got all the time in the world.

I can wait.