The doorbell jingled as I entered. An elderly couple were already moseying round the shelves, picking up and replacing all manner of cheap gadgets and I was forced to wait until they moved on so I could reach the counter. I glanced up into the corner, closing my eyes and offering up a silent prayer to some random deity. Perhaps Mitch was listening.

‘Can I help you, madam?’

The CCTV camera was pointed directly at the counter; Big Brother is watching you and I thanked God for the high crime rates in North London that instilled fear into local shopkeepers. The camera seemed to be working. There was a small red light flashing on and off at regular intervals. It wasn’t a fake deterrent.

The elderly lady had put up her umbrella inside the shop, before exiting.

‘That’s very bad luck, madam,’ the fat vendor chortled before he turned his attention back in my direction. ‘Are you looking for a new mobile phone? A case perhaps?’

Before I could answer, the salesman had extricated half a dozen cheap models from under the counter and spread them across the glass surface. I went to the front door and turned the Open sign to Closed.

‘I’ve no cash, madam. I banked it all yesterday. We have cameras everywhere.’ The owner pleaded while holding his hands in the air as if in some Western spoof.

‘I need your help,’ I said. I pulled out the receipt which I’d kept under lock and key since the night of the murder. It was the one I’d found down the side of the armchair in Mitch’s flat.

‘On this date,’ I pointed at the small piece of paper, headed up Handy Mobiles with the address clearly visible underneath, ‘you sold a phone, a pay as you go to a gentleman. You can see the make and model number here.’ My forefinger stabbed at the date.

I refused to let go of the piece of paper, which was mine, and Oliver’s, get-out-of-jail free card. The man in front of me was sweating. I could sense his fear. He ran the back of his hand across his brow and wiped away the drips. It took a second before he answered.

‘Yes I remember very clearly that particular sale,’ he said, confident with his speedy retort. ‘A strange guy wearing a dark baseball cap. Paid in cash. Why do you want to know?’ If I was amazed at how certain he was, I didn’t comment. I stuck to my original plan.

‘CCTV. I need to see the footage. Now. It’s really important.’ The windows had steamed up and I went over and ran my hand across the centre pane. I flicked my eyes from side to side, up and down the street.

‘Shit.’ A bus stop was located right outside the front door and a bus pulled alongside, blocking my view.