As planned, we'd crawled to a point between two ground-floor windows. A utility box the size of a coal bunker was set against the wall. It was an ideal location for the stuff we were going to leave behind.

Fingers shielding the lens of his mini-Maglite, Charlie opened the utility box with a square lug key and had a quick look inside.

Half Arse had his pistol out; he kept his eyes on the windows and his ears everywhere else. He'd had a buttock shot away during an op a few years back, and right now I wondered if it meant his arse was only half as cold as mine. His wife wanted him to have an implant so he didn't scare the kids when he took them swimming, but they weren't available on the NHS, and he refused to go private. 'I'm too tight-arsed' was his standard joke. 'Or rather, tight half-arsed…' Nobody ever laughed. It wasn't very funny, and nor was he.

We knew that everyone in the various Pods [tactical operations] would be watching the thermal and IR imagery of us at work, beamed down to them by the P3. We wanted to make sure it was a job well done; don't mess with the best was the message we wanted to transmit – though right now it was the last thing any of us was worried about; personally, I just wanted to do the business and get away alive. This was my last job before I left the Regiment. It would be the mother of all ironies if I got dropped or injured now.

I eased my day sack off my back. A distant voice inside the building shouted out something but we ignored him. We'd only react if someone was actually shouting that they'd spotted us; otherwise, we'd be stopping and starting every five minutes. You just have to get on with it until you know there is a definite drama. That was what Half Arse was here for.

Charlie had worked out where he wanted to fix the device. He pressed a thumbnail into the wood at almost ground level and gave me a nod. I brought out a pyramid from my day sack, seven inches high and made of alloy. Instead of a peak, it had a hole, and at each of the four corners was a fixing lug.