“Not a soul. We were alone all the evening.”

“However,” said Thorndyke, “if you are innocent—as I am assuming—the evidence against you must be entirely circumstantial and your alibi may be quite sufficient. Have you any idea of the grounds of suspicion against you?”

“Not the faintest. The papers said that the police had an excellent clue, but they did not say what it was. Probably some one has given false information for the——”

A sharp rapping at the outer door cut short the explanation, and our visitor rose, trembling and aghast, with beads of sweat standing upon his livid face.

“You had better go into the office, Belfield, while we see who it is,” said Thorndyke. “The key is on the inside.”

The fugitive wanted no second bidding, but hurried into the empty apartment, and, as the door closed, we heard the key turn in the lock.

As Thorndyke threw open the outer door, he cast a meaning glance at me over his shoulder which I understood when the newcomer entered the room; for it was none other than Superintendent Miller of Scotland Yard.

“I have just dropped in,” said the superintendent, in his brisk, cheerful way, “to ask you to do me a favour. Good evening, Dr. Jervis. I hear you are reading for the bar; learned counsel soon, sir, hey? Medico-legal expert. Dr. Thorndyke’s mantle going to fall on you, sir?”

“I hope Dr. Thorndyke’s mantle will continue to drape his own majestic form for many a long year yet,” I answered; “though he is good enough to spare me a corner—but what on earth have you got there?” For during this dialogue the Superintendent had been deftly unfastening a brown-paper parcel, from which he now drew a linen shirt, once white, but now of an unsavoury grey.

“I want to know what this is,” said Miller, exhibiting a brownish-red stain on one sleeve. “Just look at that, sir, and tell me if it is blood, and, if so, is it human blood?”