‘Can you run all the numbers alongside each other, cross-referencing and looking for anything that appears on the bills for all the numbers we have so far? I’m looking for anyone that appears between our dirty cop and dirty NCA Man. My guess is we have a group of cops or agents who share the same taste in women,’ Tom said.

Pet continued to work at the computer while Tom checked the window of the flat opposite with his binoculars. The laser-listener remained quiet and there was no movement at the windows.

‘Okay. I have three numbers that all seem to call each other as well as calling the Brankos and Ana. One is the dirty cop, one is dirty NCA Man, the other ends in 419. I’ll check that one out now.’ Her face was a picture of concentration as she typed away.

Tom was seriously impressed with her efficiency and could see why she’d be a prized asset of the CIA. The intelligence she was finding in seconds would take weeks through official channels.

‘It’s a burner phone again: most of its calls are to the other two plus several to the Brankos and Ana,’ she said.

An idea flashed into Tom’s head.

‘Can you get cell sites for all the phones? Use time parameters that will give us the best indications of where the phone is during work hours and where it is first thing in the morning and last thing at night.’

That was a classic investigator’s trick. The first call in the morning and last call at night generally indicated the area someone lived. During the day, if the phone was static long enough, then that would indicate where someone worked.

‘It’s a good job I have good e-discovery software, Mr Detective, or this would take forever. Hold on.’

A minute or so later, she ran her fingers through her hair and yawned. ‘Okay, cell sites for Dirty Cop put it hitting cell sites during work hours in London NW6, Kilburn. There’s a mix of masts but best guess is Salisbury Road. After-hours seems to be in Watford.’

Tom’s eyes did not display the impact of this news.

‘That’s Kilburn nick; that’s my police station. The bent bastard is a colleague. Who’s next?’ His matter-of-fact tone was a little unnerving.

‘NCA Man’s work hours we know; out-of-hours he’s in Hemel Hempstead.’

Tom nodded and said nothing.

‘Last man, 419 number: working hours is IG1 postcode, Ilford Town. Looks like he’s sleeping at an address in St Albans.’

‘That’s Ilford Police Station, where Adebayo was in custody. I’m laying bets that’s who erased the SD card.’

So, there it is, thought Tom. Three corrupt public officials, all living close to each other in Hertfordshire, all using the same prostitutes, all eminently corruptible because of their lifestyles, and all with the opportunity to carry out what had happened.