Lesley was short, blonde and impossibly perky, even when wearing a stab vest. We’d gone through basic training at Hendon together before being transferred to Westminster for our probation. We maintained a strictly professional relationship, despite my deep-seated yearning to climb into her uniform trousers.

Because we were both probationary constables, an experienced PC had been left to supervise us — a responsibility he diligently pursued from an all-night café on St Martin’s Court.

My phone rang. It took me a while to dig it out from among the stab vest, utility belt, baton, handcuffs, digital police radio and cumbersome but mercifully waterproof reflective jacket. When I finally managed to answer, it was Lesley.

‘I’m going for a coffee,’ she said. ‘Want one?’

I looked over at the covered market and saw her wave.

‘You’re a life-saver,’ I said, and watched as she darted off towards James Street.

She hadn’t been gone more than a minute when I saw a figure by the portico. A short man in a suit tucked into the shadows behind the nearest column.

I gave the prescribed Metropolitan police ‘first greeting’.

‘Oi!’ I said. ‘What do you think you’re doing?’

The figure turned and I saw a flash of a pale, startled-looking face. The man was wearing a shabby, old-fashioned suit complete with waistcoat, fob watch and battered top hat. I thought he might be one of the street performers licensed to perform in the piazza, but it seemed a tad early in the morning for that.

‘Over here,’ he said, and beckoned.

I made sure I knew where my extendable baton was and headed over. Policemen are supposed to loom over members of the public, even helpful ones. That’s why we wear big boots and pointy helmets, but when I got closer I found the man was tiny, five foot nothing in his shoes. I fought an urge to squat down to get our faces level.