Inspector Whyland, walking through Praed Street that evening about ten o’clock, heard a cheerful voice bid him good evening, and turned to find Mr. Ludgrove by his side.

“Hullo, Mr. Ludgrove!” he exclaimed. “I called at your place just now, and found it shut up. I thought you were away.”

“I have been taking my usual evening stroll,” replied the herbalist. “Won’t you come in? I’m on my way home now.”

With scarcely a moment’s hesitation, Whyland accepted the invitation. There was always the chance that the herbalist might make some suggestion which would throw light on this latest problem. He waited until they were seated in the familiar back room before he asked the inevitable question. “You’ve heard what happened here this morning, I suppose?”