I used to worry that he’d sussed us out because of the way he’d withdraw large amounts of cash and then live off that for a couple of weeks. But soon the siren call of instant card payment caught up with him, and now he chips and pins like the rest of us. I scanned his transactions and noted some regular payments to a branch of Greggs on Kilburn High Road at the same time every afternoon. After that it was a simple matter of ‘borrowing’ a pool car and having my coffee out.

The only car available was a bloody Silver Astra which was so obviously an unmarked police car that it might as well have had an orange BILL ON BOARD sticker in the rear window. So I parked it around the corner. And, after picking up a coffee and steak slice for myself, took my place at the bus stop opposite. Bus stops are great temporary stops for surveillance since they give you a legitimate reason to be standing around looking bored and the adshell shelters you from the rain.

Despite the weather, the High Road was heaving with schoolkids, mums and buggies and people out shopping. Given the rain, I’d swapped out my suit jacket for my stakeout hoodie, which rendered me effectively invisible.

Given that Zach’s attitude towards punctuality had always been one of stunned incomprehension, the time of his daily transactions were remarkably consistent – I suspected that he was on his break from a job. If so, it was amazing he’d held it for the three weeks he’d been making the pickups. Five days having been the longest he’d previously held a job for – at least that we had records about.

Right on time I spotted him coming up the street from the direction of the station. He was the same skinny wretch, hands jammed in the pockets of his worn jeans and, like me, hoodied up against the rain and random CCTV in grey Adidas. I thought he was going to walk right past me, but before he reached the bus shelter he turned sharply and skipped across the road to the Greggs.

I scoffed the last of my steak slice as I waited for him to come back out. I had been planning to catch him in the queue, but now I was curious to know what he was up to.

Whatever it was, it seemed to involve three large carrier bags worth of food. Not even Zach, I thought, can eat that much – or at least not in one go.

I followed him around the corner and down Belsize Road, which runs beside the railway tracks and is one of those places where you can see the industrial heritage of London being swiftly gentrified into luxury offices for hire. Although this process hadn’t quite reached the ramshackle collection of one storey garages half-way down the street on the railway side.