“Well, sit down, and tell us all about it,” said the Professor, motioning Hanslet towards a comfortable chair. “You will relieve the tedium I am feeling at having nothing to do.”

Hanslet sat down, and, as he did so, looked enquiringly at the Professor. “You say you’ve nothing to do, sir? Well, I’m very glad to hear that. The truth is that I didn’t come here to tell you my experiences. As a matter of fact, I meant to take a month’s leave when I got back, but the Chief asked me to wait a bit and take over a case which has been puzzling the Yard for several months. And I wanted to ask your advice, if you would be good enough to listen.”

The Professor rubbed his hands together briskly. “Excellent, excellent!” he exclaimed. “I told you this morning, Harold, that a problem was bound to turn up before long. By all means tell me your difficulties, Inspector. But let me beg of you to keep to facts, and not to digress into conjecture.”