I hadn’t been able to protect him, no. The next best thing was to avenge him. He was going to be buried on Monday, and I knew I couldn’t go. To create some fitting symmetry, perhaps, I had decided that the night before his funeral I would murder McGee.

Once, when Big Jacky had been to some church jumble sale, he brought me back a job lot of Agatha Christie detective stories. I was about twelve years old, and I started working my way through them very methodically. I used to try and guess who the murderer was shortly after being introduced to the entire cast of characters. It took a lot of willpower not to flick through to the end and find out straight away if I was right.

At first, I would always guess the most obvious person, the one with the creepy smile and a long-held grudge and a touch too much brilliantine on their hair. Then – once I realised that it was never them – I started guessing the least obvious instead, the real trouper who was busy making all the funeral arrangements and had been a loyal friend to the deceased through thick and thin.

It usually wasn’t that one either, though. She was sly enough, Agatha Christie, and the killer was mostly some character who had just wandered in stage left, someone you actually hadn’t thought about that much but considered pretty okay if you did.

In real life, of course, the killer often really is the most obvious person, the one with a motive the size of a skyscraper. That’s why most genuine murder hunts end up catching The Last Person to See The Victim Alive, or the Person Who Stands To Gain Thousands of Pounds From The Life Insurance Policy. Most fat-bellied, case-hardened detectives already know that life is much simpler and killers are more brutishly transparent than in an Agatha Christie novel.

I pictured the police interviewing the Whartons, and realised that they would say about me, with no ill intent, ‘Well, he mostly kept himself to himself.’ I really did. That wasn’t good: I was already a case-notes cliché, and I hadn’t even done anything yet. Perhaps I should have invested more energy in appearing friendly and outgoing when I had the chance. It was too late to change now. It would seem very odd if I returned to London from my good friend’s hospital bed having been transformed into a compulsive extrovert. It would look incongruous, as though I had been elated by the misfortune of others.