‘Nice empty flat, no one to hear us,’ Callum crooned into her ear. ‘Though you do know … as soon as you’re ready to move in … Leah’ll go when I say, it could be just the two of us always—’

Tamsin pulled away. ‘We were having such a nice time,’ she said, preparing to mount the podium of their favourite argument; but she was interrupted by a shout from the other end of the platform.

‘Hey there! Tamsin, Callum!’

Bounding towards them with irregular, exhausted strides was a very red-faced Chris.

‘Changed my mind,’ he panted, raising his voice above the incoming train. ‘Whew. Didn’t think I’d catch you, I had to run all the way back up the escalators.’

‘You didn’t have to, we really didn’t mind you going,’ Tamsin told him as they shuffled onto the train.

‘I know, I just somehow didn’t feel like it any more,’ Chris said; and Tamsin experienced a guilty throb of triumph.

‘So what do you think of the American system?’ Callum said to Chris once the doors had closed, continuing an earlier conversation about the pros and cons of six-month deployments.

Tamsin let them talk. Too tired and tipsy to follow the arguments, she stared idly up at a poster informing her she was ‘living proof that posters get read’. She only zoned back into the conversation at Charing Cross, when Callum needed her to remember a name.

‘You know Tam, that little wine bar just above the station here – the one you took me to on our second date.’ He turned to Chris. ‘Sort of a cellar, very dark and atmospheric.’

‘Do you mean Gordon’s?’ Chris asked.

‘Gordon’s, that’s it! So you know it then. Isn’t it fantastic?’

‘Yes, a real gem,’ agreed Chris, with a quick wink at Tamsin. The secret about their long-ago meeting on the tube seemed like a private joke to him now.

Tamsin looked away, feeling sick; but once again, Chris failed to notice her discomfort. He saw only her beauty and her freshness, the satin sheen on her heavy eyelids, the simplicity of her plain white shirt (so much more appealing to him than Leah’s dressed-up look). She hadn’t noticed that one of her buttons had come undone; from his superior vantage point, Chris could see the scalloped edge of her bra. It was his turn to look away. With this girl, even a glimpse of her underwear made him feel guilty. He recalled her squeamishness during the conversation about wanking: it signalled a fundamental purity, the saint-like status she held for him. She and Callum formed the perfect couple, the bond between them inevitable, unshakeable.