‘Francis,’ Jessica was saying, ‘just look at it . . . it’s not worth the risk . . .’

‘Jessica, we were prepared to do this. It’s what we wanted.’

‘I was going to do it when I thought it was possible. But just look at that space . . .’

Whilst we talked, I was aware of a second police car arriving from King’s Parade. There were more voices in the street around the Senate House. I had hoped that the policeman’s claim to have us surrounded was a vain boast designed to coax us down, but I could now see it was not. The beams of torches appeared in the garden by the Old Library; they lanced the shadows, hemming us in. Lisa wandered away from the argument and peered brazenly down at our tormentors. Michael, Francis and Jessica continued to argue.

Then there was the sound of feet hitting the rooftop opposite, and a cry from the street below. Someone shouted, ‘Quick, they’re going to fall . . .’

Lisa was standing on the opposite side of the gulf. ‘Stop pissing about and do it,’ she said, and with that moved away across the roof of Caius to clear a space for the next landing.

There was no time for the safety rope now. We looked at one another, and Michael peeled away from the group. He stood for a few seconds at the far edge of the roof, and stared grimly at the balustrade. Then he put his head down like a bull and thundered for the gap. As he hit it, he launched his graceless body through the air, his legs stretched out in front like a pudgy child doing the long jump on sports day, and came down on the other side with such a thud I thought he must have injured himself. He rolled upright with an audible grunt, and turned back to face us across the gulf. Now there was uproar in the street below, and over the city we could hear the wail of the fire engine, bearing the ladder that would seal our fate once and for all. Jessica was breathing hard with fear, but she rose to her feet and shuffled with a gallows walk to the start of her run up. Francis stood in her way. In that instant, I could tell they were alone together, risen above all the danger and the lights and the sirens to a place where only the two of them existed.

‘You know I will stay here with you, don’t you?’ he said. ‘If you don’t want to do it, I will stay with you when they come.’

‘I know,’ she said, ‘now please move.’

She ran as fast as she could, and jumped. She had judged the distance poorly, and she had to break stride before she hit the balustrade. Her natural agility saved her from tripping, and pitching forwards over the roof into the darkness, with the cobblestones waiting at the bottom. Her jump was a desperate lunge. I felt my heart stop beating as I watched her. She hit the ledge of the roof at Caius, and for a moment she hung there on the edge, her long arms pinwheeling in the wind. Michael and Lisa darted forwards to grab her, and they took her wrists just before gravity bit, and yanked her forwards on to the roof. A gasp laced with screams went up from the crowd below as if at the antics of a tightrope walker.