Grace stared at the banknotes she was clutching in one hand, then at the shock prod in the other, then down at Rennie, then up at Ben. ‘I don’t—’

He said, ‘I do. Because if you’re an officer playing by the rules, you’ve got to account to your superiors for every time you use your Taser. These two were working off the books. Hence the need to keep it under the table and improvise a little. Hence also the other item of kit they’re not using tonight.’ He pointed. ‘Look at their uniforms. No body cams. Most forces are issued them now, including yours. But this was one “arrest” they didn’t want anyone to see.’

He left her struggling with her inevitable conclusions and went back over to the slumped heap that was PC Murray Brown. The phone that the cop had used to make his call moments earlier was still in his coat pocket. Ben fished it out. ‘Just like he was using this to tell his bosses that he’d found us, instead of calling it in by radio. One look at our faces, they knew it was us, because they’d been tipped off in advance. It’s a no-brainer, Grace. No other way to see it. Now do you understand?’

Ben checked the phone and saw that Brown’s call had been to another mobile. He would have bet all the cops’ payoff money that the number belonged to a disposable pay-as-you-go job, bought for cash, no names, no questions. The call record showed that several more calls had been made that day, to and from the same number. Nothing before then.

Grace said, ‘Yeah, I think I do understand. So what the hell are we going to do now?’

‘Much as I’d love to make a citizens’ arrest and watch these chumps getting dragged off to jail, we have no way of knowing who else in the local force has been bought off. So I vote we get out of here. But first I want to make sure our friends Murray and Dougie can’t follow us, when they wake up.’