Aaron took a pakora from the plate Joel offered him and dipped it in fragrant sauce, thinking hard. “This is astonishing from you both. What I’m wondering is how we work it. It can’t disappear into a Home Office confidential enquiry.”

“They wouldn’t, surely, sir,” Challice said. “It’s murder.”

“Strictly speaking, this only proves that Colthorne owed Knight money and lied about it. It’s obviously bad and the inference is clear but the higher-ups might well conclude that a prosecution would struggle to prove murder at this distance. And there’s still no concrete evidence that Marks was murdered, and the defence could make hay with that. Colthorne lied about his gambling debt from the best of motives, the conviction of Sammy Beech was made on strong evidence and has not been quashed, he paid Marks’s blackmail and intended to continue doing so as penance, and this entire prosecution stems from a drunkard slipping and falling on a rainy night.”

“Oh,” Challice said, deflating. “Do you think so?”

“It’s what the defence will argue. Whereas the prosecution will need to cast Colthorne as an out and out villain, a murderer given high authority in the Met for years under the noses of his colleagues and superiors. The Commissioner won’t like that at all.” He grimaced. “I’m also aware that if this comes from me, Colthorne might argue a disaffected officer trying to get revenge for his own disgrace. That could muddy the waters to the point where a prosecution might seem very hard to achieve.”

“Helen said he threatened you,” Joel said.

“Unpleasantly. He said I could look to have my various wrongdoings all over the papers.”

“Not via me. I told Sabini what we’d agreed and nothing else. If Colthorne said more, he’s a damned liar.”

Joel sounded ferocious. And he hadn’t caved. He’d stood up to Darby Sabini and lied to his face, for Aaron, and quite suddenly Aaron felt something crack inside.

“Aaron? You all right?”

“Yes. Yes. I just— I don’t know what I did to deserve you. Either of you. I have never felt so alone in my life as I did this morning, and all the time you two were doing this when you should have been watching your own backs.”

“I am watching my back; that’s why we’re meeting here,” Challice pointed out. “You’re not wrong, Mr. Fowler. We don’t want this to be bogged down by the DDI accusing you; the Commissioner would never tolerate all that dirty linen in public.”

“Could you do it?” Joel asked her.