The man in the corner cocked his funny thin head on one side and looked at Polly; then he took up his beloved bit of string and deliberately untied every knot he had made in it. When it was quite smooth he laid it out upon the table.

"I will take you, if you like, point by point along the line of reasoning which I followed myself, and which will inevitably lead you, as it led me, to the only possible solution of the mystery.

"First take this point," he said with nervous restlessness, once more taking up his bit of string, and forming with each point raised a series of knots which would have shamed a navigating instructor, "obviously it was impossible for Kershaw not to have been acquainted with Smethurst, since he was fully apprised of the latter's arrival in England by two letters. Now it was clear to me from the first that no one could have written those two letters except Smethurst. You will argue that those letters were proved not to have been written by the man in the dock. Exactly. Remember, Kershaw was a careless man — he had lost both envelopes. To him they were insignificant. Now it was never disproved that those letters were written by Smethurst."

"But — " suggested Polly.

"Wait a minute," he interrupted, while knot number two appeared upon the scene, "it was proved that six days after the murder, William Kershaw was alive, and visited the Torriani Hotel, where already he was known, and where he conveniently left a pocket-book behind, so that there should be no mistake as to his identity; but it was never questioned where Mr. Francis Smethurst, the millionaire, happened to spend that very same afternoon."

"Surely, you don't mean?" gasped the girl.

"One moment, please," he added triumphantly. "How did it come about that the landlord of the Torriani Hotel was brought into court at all? How did Sir Arthur Inglewood, or rather his client, know that William Kershaw had on those two memorable occasions visited the hotel, and that its landlord could bring such convincing evidence forward that would for ever exonerate the millionaire from the imputation of murder?"

"Surely," I argued, "the usual means, the police — "

"The police had kept the whole affair very dark until the arrest at the Hotel Cecil. They did not put into the papers the usual: 'If anyone happens to know of the whereabouts, etc. etc'. Had the landlord of that hotel heard of the disappearance of Kershaw through the usual channels, he would have put himself in communication with the police. Sir Arthur Inglewood produced him. How did Sir Arthur Inglewood come on his track?"

"Surely, you don't mean?"

"Point number four," he resumed imperturbably, "Mrs. Kershaw was never requested to produce a specimen of her husband's handwriting. Why? Because the police, clever as you say they are, never started on the right tack. They believed William Kershaw to have been murdered; they looked for William Kershaw.

"On December the 31st, what was presumed to be the body of William Kershaw was found by two lightermen: I have shown you a photograph of the place where it was found. Dark and deserted it is in all conscience, is it not? Just the place where a bully and a coward would decoy an unsuspecting stranger, murder him first, then rob him of his valuables, his papers, his very identity, and leave him there to rot. The body was found in a disused barge which had been moored some time against the wall, at the foot of these steps. It was in the last stages of decomposition, and, of course, could not be identified; but the police would have it that it was the body of William Kershaw.

"It never entered their heads that it was the body of Francis Smethurst, and that William Kershaw was his murderer.

"Ah! it was cleverly, artistically conceived! Kershaw is a genius. Think of it all! His disguise! Kershaw had a shaggy beard, hair, and moustache. He shaved up to his very eyebrows! No wonder that even his wife did not recognize him across the court; and remember she never saw much of his face while he stood in the dock. Kershaw was shabby, slouchy, he stooped. Smethurst, the millionaire, might have served in the Prussian army.

"Then that lovely trait about going to revisit the Torriani Hotel. Just a few days' grace, in order to purchase moustache and beard and wig, exactly similar to what he had himself shaved off. Making up to look like himself! Splendid! Then leaving the pocket-book behind! He! he! he! Kershaw was not murdered! Of course not. He called at the Torriani Hotel six days after the murder, whilst Mr. Smethurst, the millionaire, hobnobbed in the park with duchesses! Hang such a man! Fie!"

He fumbled for his hat. With nervous, trembling fingers he held it deferentially in his hand whilst he rose from the table. Polly watched him as he strode up to the desk, and paid twopence for his glass of milk and his bun. Soon he disappeared through the shop, whilst she still found herself hopelessly bewildered, with a number of snap-shot photographs before her, still staring at a long piece of string, smothered from end to end in a series of knots, as bewildering, as irritating, as puzzling as the man who had lately sat in the corner.