“I’m rather amazed,” said the Inspector, his voice even quieter than usual, “that nothing has turned up to focus the inquiry. In the average murder case there are numerous lines to be explored, even if the right one is not hit upon immediately. But in this affair there appears to be nothing whatever on which to concentrate.”

“That fact in itself, I should say,” rejoined Vance, “constitutes a distinguishing characteristic of the case which shouldn’t be overlooked, don’t y’ know. It’s a clew of vital importance, and if only we could probe its significance I think we’d be on our way toward a solution.”

“A fine clew that is!” grumbled Heath. “ ‘What clew have you got, Sergeant?’ asks the Inspector. ‘Oh, a bully clew,’ says I. ‘And what is it?’ asks the Inspector. ‘The fact that there ain’t nothing to go on!’ says I.”

Vance smiled.

“You’re so literal, Sergeant! What I was endeavoring to express, in my purely laic capacity, was this: when there are no clews in a case—no points de départ, no tell-tale indications—one is justified in regarding everything as a clew—or, rather, as a factor in the puzzle. To be sure, the great difficulty lies in fitting together these apparently inconsequential pieces. I rather think we’ve at least a hundred clews in our possession; but none of them has any meaning so long as it’s unrelated to the others. This affair is like one of those silly word-puzzles where all the letters are redistributed into a meaningless jumble. The task for the solver is to rearrange them into an intelligible word or sentence.”

“Could you name just eight or ten of those hundred clews for me?” Heath requested ironically. “I sure would like to get busy on something definite.”

“You know ’em all, Sergeant.” Vance refused to fall in with the other’s bantering manner. “I’d say that practically everything that has happened since the first alarm reached you might be regarded as a clew.”

“Sure!” The Sergeant had lapsed again into sullen gloom. “The footprints, the disappearance of the revolver, that noise Rex heard in the hall. But we’ve run all those leads up against a blank wall.”

“Oh, those things!” Vance sent a ribbon of blue smoke upward. “Yes, they’re clews of a kind. But I was referring more specifically to the conditions existing at the Greene mansion—the organisms of the environment there—the psychological elements of the situation.”

“Don’t get off again on your metaphysical theories and esoteric hypotheses,” Markham interjected tartly. “We’ve either got to find a practical modus operandi, or admit ourselves beaten.”