Aaron might have asked himself the same. He’d spent the last fortnight, since that catastrophic, wonderful evening with Joel, in surreptitious efforts to observe his superior, as well as pursuing the Marks case, and looking back at the Sammy Beech trial. He’d let other things slide; he’d asked questions that must have seemed meaningless; he’d probably appeared shifty to his colleagues, because he was concealing something huge and the discomfort of it doubtless showed in everything he did.

And he’d achieved damn all. He hadn’t found anything to back up Joel’s intuition on Colthorne’s handwriting, and every futile day and sleepless night was chipping away at his confidence. Maybe he was a gullible fool, taking the word of a fraud or a fantasist and destroying his career over a chimera. Maybe Marks’s death was really an accident, or a killing that had nothing to do with the DDI, and Sammy Beech’s name had cropped up by sheer chance, and if favours were being done to gangs it was at a lower level, and all his unnerving feelings of being cast in a role he didn’t want were just his own awkwardness.

He’d felt a soul-chilling certainty when he’d seen Colthorne’s hand labelled with that lethal seven. He needed to hold on to that.

He stiffened his spine, literally and metaphorically. “Sir, there are a number of suspicious circumstances in the Marks death—”

“The man was drunk, the night dark, the path slippery, the injury consistent with a fall, and the body not robbed. What is suspicious here? Have you witnesses?”

“No, sir.”

“Then what are these circumstances?”

“According to the doorman at his office, someone came in—with keys—on the night of the murder and went up to the first floor, where Marks’s office is. Marks’s keys haven’t been found. And his notebooks for the last three months are missing, meaning we can’t establish the cases he was working on when he was killed, or where his recent flush of wealth came from. That all seems highly suggestive, sir.”

Colthorne tipped his head. “As far as it goes, but it isn’t going far enough. Have you any reason to suppose the man who came in wasn’t Marks himself?”

“The medical examiner believes he went in the water some time between ten and midnight. The doorman thought that the man who came in did so between midnight and two.”

“Where is this office?”

“Macclesfield Road.”

“That’s minutes from the canal, and you know how loose medical timings can be, especially with a body in the water. Not to mention that keys can fall out of pockets. I suppose you haven’t had the canal dragged?”

“No, sir. DI Davis indicated the expense wouldn’t be approved.”

“Not without more grounds. Where have you looked for these missing papers?”