There was a little stack of blank cards on the desk in front of him: homemade cards featuring one of his own close-up, black-and-white photographs of frost fibres on a sprig of yew. These were for his colleagues; Callum had intended to spend break-time writing them. Now, on an impulse, he took a card from the pile and scribbled a message inside it. ‘Happy Christmas, Sophie. You’ve been a joy to teach.’ As soon as he’d written these words he regretted them. ‘A joy to teach’ – what a cliché. But it would look worse if he crossed it out, and he didn’t have enough cards to use another.

All this took a matter of seconds: when Callum left the classroom, Sophie was yet to reach the swing doors that led out to the schoolyard. Callum sprinted down the long corridor to join her, and when he handed her the Christmas card, the pleasure in her face was worth all the indignity and impropriety of running to catch up with a pupil.

* * *

Following his new resolution to be (temporarily) the perfect boyfriend, Chris went all out with his Christmas presents for Leah. Tamsin helped him choose a cashmere cardigan and a simple gold necklace with a tiny diamond at its centre. On Christmas day itself, he had an enormous box of roses delivered to Leah’s family home in Birmingham.

Each of these presents was, in its own way, repugnant to Leah. The cardigan was made in China. The diamond was untraceable, but she had serious doubts about it being ethically sourced. Her objection in these two instances wasn’t so much the damage done to factory workers or diamond miners, but the thoughtless consumerism that cheap labour represented. It seemed to her like another form of pollution. She imagined all the wardrobes and cupboards and shelves of London filling up with the dark greasy sludge of unnecessary possessions, a contaminant sticking to everyone yet invisible to all but a few.

And then white roses, in England, in December: the carbon footprint was unthinkable. But the roses represented more than airmiles and high-end junk. The roses meant that her boyfriend of nearly four months knew nothing whatsoever about her.