“Which leaves Burgh, who seems … I don’t know, I keep going backwards and forwards. On the one hand he works here, so that’s one hell of a deep cover, and he seems so bumbling it wouldn’t make sense.”

“Unless that’s an act,” Hanna pointed out. “The professor’s the same way. He acts exactly how I’d act if I was a criminal mastermind trying not to look like a criminal mastermind.”

“But he’s definitely off the hook for Belloc,” Liza pointed out. “Whereas Mr Burgh has no alibi and all of the access. And …” She trailed off. There was another thought that kept creeping up on her—a silly, pointless thought that had no place in an actual criminal investigation. “And, well, and his name begins with B.”

“So did Belloc’s,” Hanna pointed out.

“Yes, but he’s dead. And part of me says that if I was the kind of shadowy kingpin who went by a one-letter pseudonym, I’d use it in all my aliases.”

“True, but maybe you’d get caught really quickly.” Hanna smiled in a way Liza couldn’t remember being smiled at in a long time.

“Either way,” Liza continued, “we know that whoever got the gun initially, it was with the person who shot Belloc at the point when Belloc was shot.” She moved the Belloc sheet into position. “And I’m as sure as I can be that it wound up in Mrs Ackroyd’s room—either because she put it there or because somebody put it there to frame her—and that she threw it out the window into the bushes underneath.”

“Because of the snow,” clarified Hanna, and she didn’t even sound like she was taking the piss.

“Right. And from there somebody picked it up. And that somebody couldn’t have been Mr Burgh, because he was with us.” Collecting the papers again, she reshuffled them into the groups who’d gone looking for the gun. “But Ruby, Lincoln, and the colonel split up before we found it, so any of them could have got there. And the professor had been out of the room earlier and had ditched Sir Richard and his aunt too, so he could have grabbed it at any time. Sir Richard probably couldn’t unless Lady Tabitha was in on it, but maybe they split up as well?”

Trying not to look too smug, Hanna said, “It’s not looking great for Ruby, is it?”