Hanslet smiled. The Professor’s passion for facts was well-known to him from past experience. “Well, I expect you know as much about it as I do,” he began. “Ever since Tovey the greengrocer was killed last November, there’s been a lot in the papers⁠—”

But the Professor interrupted him. “I should perhaps have explained, Inspector, that since last October I have scarcely opened a newspaper. My whole mind has been concentrated upon a task which is now happily finished. The name of Tovey the greengrocer is, I regret to say, utterly unfamiliar to me. I should be glad if you would treat me as one who has only lately reached this world from the planet Mars, and give me the facts without presuming that I have any previous knowledge of them.”

“Very well, Professor,” replied Hanslet. “You must have heard of a series of deaths under peculiar circumstances which have occurred in Praed Street, not half a mile away from here? Why, I read about them in New York! They caused a great sensation.”