‘Dog bite,’ Hodges said.

The suspect was completely hidden while he pumped fuel. There was just one very brief full-height glimpse as he passed through the extreme right-hand periphery of the camera’s fisheye lens.

Hodges froze the image, and moved the magnifier to the right-hand section. It was a side view. The suspect was of average height, slim, and wearing a woolly hat and sunglasses. He had a well-kept but dark beard, and appeared to be of a dark skin tone. Possibly Asian.

‘Bingo,’ breathed Hodges.

‘I don’t know who it is but it’s definitely not Jason Waddington,’ Gillard said. ‘And there appears to be no one else in the vehicle.’ Over the next few minutes they switched methodically from one camera to the next to see if there was any view that they had missed. They only gleaned one extra piece of evidence, from the exit camera. There was a bicycle wheel visible through the rear window.

Morag Fairburn’s home in Esher was a three-bedroom semi-detached, familiar to Gillard only from the surveillance footage he had seen. Gillard arrived at 8.30 p.m. as arranged, to find lights already on. Accustomed to having to wait for the Roy family, the detective was pleasantly surprised that Morag’s BMW was already parked in the drive and the Toyota estate parked in the street outside.

She answered the doorbell immediately, a sandwich in one hand, mouth full of food, mobile phone tucked into one shoulder. She gestured to Gillard to come in. She was still in work clothes, minus shoes. The detective recognised Harry Roy’s voice on the other end of the phone, asking for various figures to be supplied. Morag gestured to Gillard to go into the lounge, and held up one hand, fingers spread. Five minutes.

The lounge was a very conventional, middle-class room. A single bookcase with as many photographs and ornaments as books, some old photograph albums, and a smallish TV. A small tortoiseshell cat was lying in a basket asleep underneath an end table. A teenage boy was visible in the kitchen, still in school uniform, looking at his phone while eating.

Morag was as good as her word, and five minutes later ended the call, and came in to sit opposite him.

‘Sorry about that. I think you know why we’re so busy. As I said, I’m more than happy for you to take the Toyota away if you think it would help.’

‘Thank you. We’ll get it towed later this evening. Is it always parked outside?’

‘Generally. I leave the key with the others by the hat stand in the hall. Not that I wear many hats. Mrs Boswell has returned the spare key, now her car’s been repaired.’

‘We did a fair bit more work tracing your vehicle, and someone was certainly driving it around before eight o’clock on the morning of Mrs Roy’s death. Are you sure you no one borrowed it?

‘Yes. I’ve had a think, and I’m sure you must be mistaken. I’ve heard that car number plates can be copied.’