The police had thought that the fact that the first man had picked up a friend off-camera diminished his plausibility as a killer. This was assuming that the two were, indeed, friends. Strike had to concede that the fact that they had been caught on film together, in such weather, and at such an hour, acting in an almost identical fashion, suggested complicity.

Allowing the footage to run on, he watched as it cut, in almost startling fashion, to the interior of a bus. A girl got on; filmed from a position above the driver, her face was foreshortened and heavily shadowed, though her blonde ponytail was distinctive. The man who followed her on to the bus bore, as far as it was possible to see, a strong resemblance to the one who had later walked up Bellamy Street towards Kentigern Gardens. He was tall and hooded, with a white scarf over his face, the upper part lost in shadow. All that was clear was the logo on his chest, a stylised GS.

The film jerked to show Theobalds Road. If the individual walking fast along it was the same person who had got on the bus, he had removed his white scarf, although his build and walk were strongly reminiscent. This time, Strike thought that the man was making a conscious effort to keep his head bowed.

The film ended in a blank black screen. Strike sat looking at it, deep in thought. When he recalled himself to his surroundings, it was a slight surprise to find them multicoloured and sunlit.

He took his mobile out of his pocket and called John Bristow, but reached only voicemail. He left a message telling Bristow that he had now viewed the CCTV footage and read the police file; that there were a few more things he would like to ask, and would it be possible to meet Bristow sometime during the following week.

He then called Derrick Wilson, whose telephone likewise went to voicemail, to which he reiterated his request to come and view the interior of 18 Kentigern Gardens.

Strike had just hung up when the sitting-room door opened, and his middle nephew, Jack, sidled in. He looked flushed and overwrought.

‘I heard you talking,’ Jack said. He closed the door just as carefully as his uncle had done.

‘Aren’t you supposed to be in the garden, Jack?’

‘I’ve been for a pee,’ said his nephew. ‘Uncle Cormoran, did you bring me a present?’

Strike, who had not relinquished the wrapped parcel since arriving, handed it over and watched as Robin’s careful handiwork was destroyed by small, eager fingers.

‘Cool,’ said Jack happily. ‘A soldier.’

‘That’s right,’ said Strike.

‘He’s got a gun an’ dev’rything.’

‘Yeah, he has.’

‘Did you have a gun when you were a soldier?’ asked Jack, turning over the box to look at the picture of its contents.

‘I had two,’ said Strike.

‘Have you still got them?’