They couldn’t think of anything.

Meanwhile, I carried on counting. Gradually, I managed to count automatically, while I was chatting or eating, and soon, in my sleep. I woke up with a number in my mind: at first, it seemed improbable. I was dubious, then convinced. Anthea told me I’d developed an aptitude which was perhaps not as extraordinary as all that; it was simply that no one had ever needed it before.

I counted my heartbeats one by one, and I soon found myself faced with huge numbers that defied mental calculations. At seventy-two beats a minute, an hour was equal to more than four thousand, two hundred, and by the end of the day I had reached over fifty thousand. It was no longer manageable. So I found a different technique: I counted seventy-two then I mentally chalked up one. I started again and chalked up two, but I was afraid of getting confused with these two different scales. Then a woman would come along and act as an abacus: I’d say one, she’d remember it, then I’d say two. She soon became unnecessary because I didn’t make any mistakes. I saw that I was keeping track of the figures accurately. Gradually, I no longer needed to say the numbers out loud. Something fell into place inside me that alerted me automatically every seventy beats. I became a human clock.

Our days lasted between fifteen and eighteen hours, with random variations. From the moment the lights were turned down, which we called the beginning of night, about six hours went by before we were awakened. That was how we established that we were living according to an artificial clock. We needed to understand why.

Emma put forward the craziest theory.

‘We’re not on Earth. We are on a planet that rotates every sixteen and a half hours.’

‘How would we have got here?’

‘How did we get into the bunker?’ I asked.

Nobody had the least idea, which amazed me.

I’d put my own lack of memories down to the fact that I’d been so young and to the women’s state of shock that Anthea had described to me, but the others knew no more than I did. Apparently, life had been going on as usual, when suddenly, in the middle of a night that had begun like any other, there’d been screams, flames, a stampede, things which I, who’d always lived in the quiet of the bunker, couldn’t begin to imagine.

‘There were strange drugs that affected the brain and created false memories,’ said Emma.

Anthea wasn’t convinced of this. There’d been all sorts of unconfirmed rumours, stories of brainwashing, genetic engineering or robots so sophisticated that they were mistaken for human beings.

‘The fact is that none of us seems to have any coherent memories that would enable us to piece together what happened. We don’t even know if there was a war,’ said Dorothy. ‘I can recall only vague images: I see flames, people running in all directions, and I think I’m tied up and frightened. It goes on for a very long time. I’m still frightened, but there aren’t even any images any more.’