I knew Jennifer would have kept copies of that video to an absolute minimum. It was too dangerous to have multiple copies of an incriminating film in circulation as Alex Bayley lay seriously injured in a hospital bed. And I was right, for once: Sean’s investigations discovered only two additional copies, in addition to the one uploaded to VideoVault: the original MP4 file, shot on a mobile device, and one other copy stored locally. No emailed copies. Too risky.

Mobile phones were strictly forbidden at school on pain of week-long confiscation. A full week of social death, in Lucy’s words, and it seemed to be an effective deterrent: Jake’s phone was where I hoped it would be, plugged in to charge in his bedroom. I unplugged it and took out the device that Sean had given me – no bigger than a memory stick, with a cable attached. Plugged it into Jake’s phone and watched as the screen unlocked and went first black, then white, a short message appearing.

Are you sure you want to restore to default factory settings? Yes/no

I hit yes – and the phone’s screen went black again as it deleted every file, every app, every picture, every video, restoring the mobile to its original newborn state. I plugged the charger back in and left it where I had found it.

Two copies left.

I went into the small study, booted up the PC and inserted the device into a USB slot.

Launch BlueScreen for PC? y/n

I hit yes.

The screen went black, flashed with lines of code several times, then beeped once, twice. The screen went blue. I pressed all the keys. Turned it off and rebooted it. Blue screen again. No cursor, no mouse, no screensaver, no nothing.

Blue screen of death, as Sean called it.

One copy left.

A few years ago, in a flap because she’d let her car insurance lapse while they were abroad, Jennifer had asked me to log into her account from this very same PC and renew her cover before they made the journey back from Gatwick. She kept all her passwords on a couple of sheets of handwritten A4 clipped into a black plastic binder.

I opened the second desk drawer and dug beneath a stack of bank statements, found the black plastic binder. Same place. Same old Jennifer. The username and password for her VideoVault account was the newest addition at the bottom of the list. I took out a cheap pay-as-you-go phone and sent a text to an identical handset – both of which would soon be on their way to a landfill site.

Ten miles away, in central London, my husband went to work at his keyboard. A text pinged on my throwaway phone two minutes later.

It’s done x