As he assembled the raw components of a new file – the hardback folder, the blank paper and an acro clip; the notebook in which he had recorded Bristow’s interview; the pamphlet from the Tottenham; Bristow’s card – he noticed the new tidiness of the drawers, the lack of dust on the computer monitor, the absence of empty cups and debris, and a faint smell of Pledge. Mildly intrigued, he opened the petty cash tin, and saw there, in Robin’s neat, rounded writing, the note that he owed her forty-two pence for chocolate biscuits. Strike pulled forty of the pounds Bristow had given him from his wallet and deposited them in the tin; then, as an afterthought, counted out forty-two pence in coins and laid it on top.

Next, with one of the biros Robin had assembled neatly in the top drawer, Strike began to write, fluently and rapidly, beginning with the date. The notes of Bristow’s interview he tore out and attached separately to the file; the actions he had taken thus far, including calls to Anstis and to Wardle, were noted, their numbers preserved (but the details of his other friend, the provider of useful names and addresses, were not put on file).

Finally Strike gave his new case a serial number, which he wrote, along with the legend Sudden Death, Lula Landry, on the spine, before stowing the file in its place at the far right of the shelf.

Now, at last, he opened the envelope which, according to Bristow, contained those vital clues that police had missed. The lawyer’s handwriting, neat and fluid, sloped backwards in densely written lines. As Bristow had promised, the contents dealt mostly with the actions of a man whom he called ‘the Runner’.

The Runner was a tall black man, whose face was concealed by a scarf and who appeared on the footage of a camera on a late-night bus which ran from Islington towards the West End. He had boarded this bus around fifty minutes before Lula Landry died. He was next seen on CCTV footage taken in Mayfair, walking in the direction of Landry’s house, at 1.39 a.m. He had paused on camera and appeared to consult a piece of paper (poss an address or directions? Bristow had added helpfully in his notes) before walking out of sight.

Footage taken from the same CCTV camera shortly after showed the Runner sprinting back past the camera at 2.12 and out of sight. Second black man also running – poss lookout? Disturbed in car theft?Car alarm went off around the corner at this time, Bristow had written.

Finally there was CCTV footage of a black man closely resembling the Runner walking along a road close to Gray’s Inn Square, several miles away, later in the morning of Landry’s death. Face still concealed, Bristow had written.

Strike paused to rub his eyes, wincing because he had forgotten that one of them was bruised. He was now in that light-headed, twitchy state that signified true exhaustion. With a long, grunting sigh he considered Bristow’s notes, with one hairy fist holding a pen ready to make his own annotations.