I’m still on morning autopilot. I wander into the kitchen, with its ATAG stainless steel hob and polished black granite worktops, and scoop a can of Whiskas into Cat’s bowl. I wash my hands, fill the kettle, and retrace my steps across the living room to the front hall, to collect two bundles of newspaper first editions, which – if they haven’t been nicked – should be in the building’s communal corridor by the door to the street. It is only when I am in my front hall that I register why the street sound has been rising and falling all morning. The front door of my flat, which gives on to the communal corridor, is ajar. It’s just a couple of inches, but open all the same.

Impossible. No matter how drunk or stoned I am, however late I come home, it is a religious ritual to make sure the door is shut, locked and bolted. I always triple check, then tug on the handle until there’s a dent in my fingers. Even after that, if there’s the tiniest trace of doubt in my head, I’ll head back and check it again, before I am able to go to sleep.

How can it be open? The thought of someone else’s hand on the knob makes me squirm. I am wearing a red sweatshirt and I pull the sleeve over my hand before touching anything. The door frame is intact, not splintered at all. There are no gouges or scratches around any of the locks. There is nothing to suggest it was forced in any way.

Could I have forgotten to lock it? Is that possible? I was a bit out of my head last night, but I am sure I went through my compulsive door-locking palaver. Could I have broken the habits of a lifetime? Did I sleep walk and unlock everything? The more I say this to myself, the less plausible it seems, especially since my keys are exactly where I always leave them, in the lower of the two deadlocks.

Cat rubs past my leg and sticks his nose out to scan the corridor in case someone will let him out to the Fields. We both plod down the corridor and I open the street door for him. Cat pauses for a moment, weighing up whether to embark on a hunt in the crisp air of a sunshiny morning or pad back to my armchair. He opts for the predatory life, as he typically does, except when the weather is foul.