And then, quite suddenly, there he was, on the telephone, inviting me round to his London flat – and that in itself was remarkable because usually if I wanted to get in, I had to ring someone else’s doorbell and pretend to be from Ocado. River Court was a low-rise block of flats built in the seventies close to Blackfriars Bridge, and Hawthorne had a space on the top floor. Space was the operative word. There was almost no furniture, no pictures on the walls, no possessions of any sort apart from the Airfix models he liked to assemble and the computer equipment he used to hack into the police database, helped by the teenager who lived one floor below.

This was something that had shocked me when I had first stumbled into Kevin Chakraborty’s bedroom and discovered him cheerfully displaying a private photograph of me and my son as his screensaver. Kevin admitted he had stolen it from my phone and then went on to explain that he had also helped Hawthorne break into the automatic number-plate recognition system used by the police in Hampshire. I hadn’t remonstrated with him, partly because he had provided us with useful information, but also because, at the end of the day, how do you pick a fight with a teenager who’s in a wheelchair? Nor had I ever mentioned it to Hawthorne. After all, this was a man who had been thrown out of the police force for pushing a known paedophile down a flight of stairs. He might have a moral compass, but he was the one who would decide which way it pointed.

He didn’t own the flat, by the way. He didn’t even rent it. He had told me that he was a caretaker, employed by a London estate agent who was ‘a sort of half-brother’. That was the thing about Hawthorne. He couldn’t have a relative who was something simple like a sister-in-law or a first cousin or whatever. He was separated from his wife, but he was still close to her. Everything about him was complicated and it didn’t matter what questions I asked because the answers led me exactly nowhere. It was all very frustrating.

The two of us were sitting in his kitchen, surrounded by gleaming chrome and pristine work surfaces. I had walked down from my own flat in Clerkenwell: we only lived about fifteen minutes apart, which made the emotional distance between us all the more striking. Hawthorne was wearing his usual combination of a suit with a white shirt, although, just for once, he had put on a grey round-neck jersey instead of a jacket. The casual look. He had offered me a cup of tea and he had been thoughtful enough to provide biscuits: four of them, to be precise; two-finger KitKats criss-crossing each other on a plate as if set up for a game of noughts and crosses. He was drinking black coffee with his ever-present packet of cigarettes close by.