I told the boys to stay quiet while I went to fetch my gun.

It usually worked. For the five minutes that it took me to get to the locker in the common-room and to return to the classroom, thirty fourteen-year-old semi-repressed hooligans could be counted on to be held in a state of fragile good behaviour, restrained only by the promise of a lesson they'd actually looked forward to. Physics in general they took to be unacceptably hard mental labour, but what happened when a gun spat out a bullet… that was interesting.

Jenkins delayed me for a moment in the common-room: Jenkins with his sour expression and bad-tempered moustache, telling me I could teach momentum more clearly with chalk on a blackboard, and that an actual firearm was on my part simply self-indulgent dramatics.

'No doubt you're right,' I said blandly, edging round him.

He gave me his usual look of frustrated spite. He hated my policy of always agreeing with him, which was, of course, why I did it.

'Excuse me,' I said, retreating, 'Four A are waiting.'

Four A, however, weren't waiting in the hoped-for state of gently simmering excitement. They were, instead, in collective giggles fast approaching mild hysteria.

'Look,' I said flatly, sensing the atmosphere with one foot through the door, 'steady down, or you'll copy notes…'

This direst of threats had no result. The giggles couldn't be stifled. The eyes of the class darted between me and my gun and the blackboard, which was still out of my sight behind the open door, and upon every young face there was the most gleeful anticipation.