Blick made no reply. He was watching the door, through which suddenly appeared a man who was not at all the sort of person that Blick expected to see. Instead of being old, and grave, and bald, and bearded, and spectacled, and dressed anyhow, the famous professor of chemistry was a smart, alert, rather military-looking man, fastidiously attired, wearing a monocle instead of spectacles, and endowed with a breezy air and cheery smile, which he bestowed freely on the two occupants of the room as he marched in and seated himself by the Chief Constable’s desk, on the edge of which he laid down two or three newspapers, heavily marked here and there with blue pencil. “Good morning—good morning!” he exclaimed. “I don’t know whether you’ll guess my business from my name—or, indeed, if you know anything about it? But I’ve been reading the newspaper accounts of this Markenmore affair, and it seemed to me, last night, that it was my duty to come here and tell you something. And first of all, to make things clear, have you had here a young man named Spindler, a chemist’s assistant, from Farsham?” “We have!” replied the Chief Constable. “Did he tell you anything in which my name came up? And if so, what?” “He told us—this is Detective-Sergeant Blick, who was with me when this man Spindler called—that a certain secret of his, respecting the preparation of some dye which he had offered to sell to Guy Markenmore, was submitted to you by Markenmore, for your expert opinion.” “Just so! It was. Markenmore got my opinion. Now—how much further had that gone?” “Gone to this,” answered the Chief Constable. “When Markenmore was murdered he had on him three thousand pounds in bank-notes, which, we believe, he was to hand over to Spindler that very morning in payment for his secret.” “Spindler was going to sell for three thousand pounds?” “He was—so he told us.” The Professor of Chemistry screwed his monocle still further into the cavity of his eye, and took a queer, keenly-inspecting glance at the two men. “Do you two believe—are you theorizing that Markenmore was murdered for the three thousand pounds?” he asked quizzically. “It, to be sure, looks rather obvious!” “There is such a theory afloat,” answered the Chief Constable. “He had that sum on him at three o’clock on Tuesday morning, and it was gone when his dead body was found a very few hours later!” “Aye!” said the Professor with a short laugh. “And something else gone with it, too! Now, look here!—I’m not a policeman, but I have some intelligence. I’ll tell you what Guy Markenmore was murdered for, and I’ll lay all the money I’ve got to a China orange that I’m right, all the time. Guy Markenmore was murdered for the Spindler formula! Dead certain!” The Professor laughed again, and slapped his elegantly-gloved hand on the desk at his side. The two listeners stared at him, and then at each other. And this time it was Blick who spoke.