“You may not have noticed it at the time, my good friend, but there was one person on this list whose alibi had no kind of confirmation. Ursula Bourne.”

“You don’t think⁠—?”

“ Dr. Sheppard, I dare to think anything. Ursula Bourne may have killed Mr. Ackroyd, but I confess I can see no motive for her doing so. Can you?”

He looked at me very hard⁠—so hard that I felt uncomfortable.

“Can you?” he repeated.

“No motive whatsoever,” I said firmly.

His gaze relaxed. He frowned and murmured to himself: “Since the blackmailer was a man, it follows that she cannot be the blackmailer, then⁠—”