Temperature coefficient. The only equation, Satnam had once laughingly told Nevis, that she could ever remember. An equation with four integers. 1021. Nevis feels her heart begin to tick and the hairs on the back of her neck stand to attention. She reaches for Satnam’s phone.

Wake up!

The seconds it takes for the passcode screen to come into view feel endless. Then, all of a sudden, there it is. Enter passcode. Carefully, with a shaking hand, she taps in the numbers 1021. And waits. And blinks. And listens to the percussion of her pulse. An elastic fragment of a second that stretches almost to breaking point before the homescreen opens on an image of the stars dotted with icons. Her whole body is trembling now, her heartbeat rackety and wild, and she locates the message icon and taps. The white message screen appears. For a moment her eyes are too busy to see anything. Blinking away the blur, she scrolls down to messages. Tash, Jessica, Luke, ‘Home’, one or two other familiar names plus a couple she doesn’t recognise. She scrolls, flips back to the night of the Valentine’s Day party. Not to the night of. Not yet. That feels too big.

A text to Jessica and Tash, 8.28 p.m.: We’re all in this. It’s time to say something. Can we talk, maybe later, at the party?

Talk, yes. Didn’t Jessica say something about this? They fell out about Jessica’s ex. Or about leaving Avon? Nevis remembers two versions and the distinct feeling that neither was quite the truth. In any case Satnam said something at the party that Jessica found unhelpful, she said. An odd word, but then the whole conversation had been odd. She recalled Jessica’s hand on her mouth, genuinely surprised that Nevis didn’t know. But what was it that Nevis didn’t know? If only she’d asked. If only she had insisted on knowing. Tash knew but Tash wasn’t telling. I should be brave, now, she tells herself. It’s time to be resolute. To stick to the course. You know how this plays out. It is a question of resolving the equations, line by line, until there are no more equations and nothing more to solve.

The next line in the solution. She screws up her eyes. Behind them, in the deep red of the retina, is the span of the bridge leading into the void.

The phone lies in the palm of her hand.

Sunday, that terrible night, is the swipe of a finger away. She can literally reach out and touch it.

Touch it, Nevis. Connect.

A blue text box appears and in it a line of white text.

To Luke, 9.57 p.m.: Can I come round? Unanswered.

And then, to a number Nevis doesn’t know, 10.25 p.m.: Had enough. Can’t live with this. Unanswered.