“One,” replied Friday, “and he only missed the meeting because his car had a flat—he lived over in Bedwyn, on the other side of the Savernake.”

“That’s unusual,” I said. “The ChronoGuard must have employed several thousand from around here alone. What does it mean?”

“It means that only those timeworkers who were living in the Wessex area have received Letters of Destiny—more specifically, only those in the Swindon branch of the timeworkers union. But this is what’s strange: It’s a shitty thing to do. If I were my future self, I wouldn’t send myself a Letter of Destiny. So then I got to thinking that maybe there was another reason I did it.”

I looked at the folder he had given me. There were copies of all the letters. Two each per ex–potential worker—one of how it might have turned out and one of how it will. There were copies of the envelopes, too, and several maps, clippings and news reports about the disbanding of the ChronoGuard—it was big news when it happened two years before.

“What’s on your mind?”

“Let me explain the scenario. You’re head of the ChronoGuard and entering your seventy-sixth year, one year from retirement. You can gaze happily back upon a long career maintaining the Standard History Eventline. You’ve defended its manipulation by the unscrupulous and altered it to protect the citizens from mischief, asteroid collision and innumerable other menaces. You are happy that you have done what you could to keep the world safe, knowing that when you hand over the ropes to next chief, the department is in good shape.”

“Okay, I can see that.”

“Good. So this is what happens: Everything, but everything you’ve worked for is to be undone. Time travel is suddenly not possible, and due to the demands of a failure in the Retro-Deficit Engineering principle, all the time engines have to be switched off. It wouldn’t be so bad if it were going to happen in 2062, the time of your retirement—but it’s not. The switch-off will be retrospective from 2002. This is a worry, because the most dangerous event of all, the one that made your career, is slated for February of 2041.”

“ HR-6984.”

“Precisely. Everything you would have been, everything you would have done, everything that made you what you were—it will all be erased. The eventline is frozen. You’re not allowed to send yourself a message, and worst of all, the disaster that made you is now going to happen because you weren’t there to stop it. A single event with a potential seven billion lives at risk, all on your shoulders. What would you do?”

“Yell? Kick some furniture? Get seriously shit-faced?”

“Mum, I’m serious.”

“Sorry.”