The Senate House lay at the very centre of the city, and so we had to adjust our normal pattern. Firstly, because of its prominence, we would have to wait until the streets were completely dead before attempting the climb. By four o’clock, we thought, the last stragglers from the clubs would have wandered home, and the rowdy queues in front of the fast-food vans in Market Square would be satisfied. The problem with leaving things so late was that by five the city would begin to wake again. This left us less than an hour to scale the building, make the jump and return to the ground in safety. There was no time for mistakes, and no room for second thoughts. Secondly, because of the risk of discovery inherent in scaling a low building of white stone in the middle of the city, we decided to conceal our identity with balaclavas. Francis gave us each one before the day of the climb, and I tried mine on in the privacy of my own rooftop. The black wool was itchy, and the area around the mouth and nose became wet and cold with spit and the moisture in my breath. Despite the discomfort, I was secretly pleased with the half-face that leered at me in my bedroom mirror when I climbed back through the window. The costume, and the fact that it was necessary for our purpose, made me feel like a real outlaw. I spent a little time pantomiming in the mirror, and making demands of imaginary soldiers in a bad Irish accent.

The climb itself went off without incident. Jessica and Lisa kept lookout from behind the cover of the thick wrought-iron railings at either end of the square. Francis found the right place to make the human ladder, and with Michael’s help he scaled my back and stood with his feet upon my shoulders. From this height he could grip the ledge at the top of the two-storey window, and lever himself up from fingertips to palms on the thin slice of stone. Squatting on the ledge with his shoulders wedged beneath the overhang he snaked his thick arms around, and disappeared over the lip of the roof. Seconds later a coil of rope slapped the stone steps on the back side of the building. We headed for the sound, and found the line wagging eagerly in the wind. We called the girls back from their posts.

‘All clear?’ Michael asked as he gave the rope a firm tug.

‘I thought I saw . . .’ Jessica was peering back into the darkness in the direction of St Mary’s Church.

‘What?’ he asked.

The note of impatience in his voice quashed Jessica’s moment of self-doubt. She was not about to display such an emotion in his presence, and shook her head, saying, ‘Nothing. Go.’

We all of us climbed the rope, just as Francis had taught us, and paused on the roof to regain our breath. The view was not spectacular, hemmed in as it was on two sides by Caius and the Old Library, but my gaze was still drawn down the length of King’s Parade, where the cobbles shone black and slick in the light of the wrought-iron street lamps, with Gothic battlements looming as far as the eye could see. It was a windy night, and my steaming breath streamed away from me after my exertions. There was no sound in the city but the rattle of an empty beer can rolling in the gutter in the street below, echoing off stone walls. Waiting there, I felt the peace and satisfaction that always accompanied the successful completion of one of our climbs. I had come to think of the silent rooftops, always bathed in darkness, as a kind of secret garden from which every waking concern was banished.