“I think I’ve known for a while,” she said, and she thought she had, although she hadn’t admitted it to herself. “Or suspected, at least. Right from the first night, you were the one who went to Mrs Ackroyd after her husband died. Somebody talked her into killing Belloc, and it could only really have been you or the reverend. Then there was the night you sent us all running out into the dark. You couldn’t have seen anybody out there because there was nobody to see, but you needed to get as many guests as possible out of the hotel so you could search our room. You’d changed your shoes by the time we got back, and there was no reason to do that if you were just going to sit on the bed quivering.”

He gave her an approving nod. “Oh, well done, Ms Blaine. You could be giving Belloc and Quirke quite the run for their money.”

“You also shot Sir Richard,” Liza went on, “to keep him from shooting Ruby. I’m not sure if that’s because you wanted to kill her yourself, or because you were worried that she still had information you needed.”

“The latter.” The professor smiled quite calmly. “I’m a practical man, not a vindictive one.”

This seemed slightly disingenuous. “You’re still planning on killing her, though?”

“But for entirely practical reasons. One simply can’t let one’s associates go around stealing from one. It’s bad for business.”

Liza gave a begrudging wince. “I suppose that’s fair. And … I guess the same applies to us?”

“No witnesses, I’m afraid.”

It wasn’t the most comforting answer, but at least it was an honest one. “That doesn’t give us much incentive to tell you where we’re hiding your bank details.”

The professor glanced at the safe. “I’d be willing to bet a reasonable sum of money that they’re in there.”

“And how will you get them out?”

“Oh, please, I’m a master criminal. Do you really think a cheap safe in a hotel is going to stop me?”

He was, Liza had to admit, right. But he also hadn’t just shot them both dead, which suggested there was something else going on. “No,” she tried, “but I think you’ve realised that once you fire that gun, you’ll have about six minutes to get the safe open, grab whatever it is you think you’re going to find in there, and then be out and wandering around the hotel looking innocent, and I don’t think you’ve got time. This isn’t like faking a suicide where you can do all the work in advance.” A thought struck her. “And that was sloppy, by the way. Putting the gun in the wrong hand.”