Joel and Challice were seated at a table laden with nibbles and snacks for a small army. Aaron stared blankly at them. “Challice? What are you both doing here? I told you—”

“Shut up, sit down, look at this,” Joel said, his voice quivering with excitement. “Look.”

Aaron took the paper he held out. He recognised the handwriting very well indeed.

I, John Colthorne, promise to pay Thaddeus Knight the sum of four thousand four hundred pounds...

“What the,” he managed. “What.”

“It’s his note of hand,” Challice said. She was vibrating almost as visibly as Joel. “The DDI owed Knight a fortune as of the third of March 1917. Knight was murdered on the fifth. And Mr. Colthorne claimed that they only knew each other casually and played for small sums. Four thousand four hundred pounds isn’t casual.”

It was something like ten years of a DI’s salary. Aaron passed his hand over his face and felt the tremor. “If Colthorne didn’t declare that as an interest—he can’t have, he’d have been treated as a suspect—”

“So he killed Knight, framed up Sammy Beech, and lied through his teeth so your lot let him lead the investigation,” Joel said. “Sees Beech hang and sits back feeling safe—”

“Until Marks comes up with this. Where did he find it? Wait: where did you find it?”

“Marks’s landlady, Mrs. Trotter,” Joel said smugly. “I did her a couple of readings and said rude things about the police, after which she ate out of my hand. Marks gave her the file and notebooks for safe keeping about a fortnight before his death, with strict instructions not to trust the police. She was supposed to post them to Beech’s family in Canada if anything happened to him, but he hadn’t passed on the address. She was just holding on to them, so we had a nice talk, and she agreed to give them to me.”

“Joel,” Aaron said helplessly.

Joel grinned at him, ochre eyes crinkling with glee. “Thank Helen. It was her idea to go back to the landlady.”

“Joint effort,” Challice said. She and Joel both had tin cups of lassi: they clinked them together. “Although we mostly owe this to Gerald Marks. Knight had left a briefcase in the lost property at Paddington, would you believe? Apparently Marks found out earlier this year that he sometimes did that as an alternative to a safety deposit box, and spent God knows how long going through every lost property in London. And, if you need any more, his latest notebook says he tapped Colthorne for two hundred pounds. That was eight days before he died.”

“We’ve got him.” Aaron couldn’t quite believe it. “We’ve got him.”

“Damn right,” Joel said. “You have to have some of these things before I eat them all, by the way, they’re incredible.”