“Say, now, Dr. Thorndyke,” she exclaimed, “have you gotten something to tell us?”

“I have a suggestion to make,” replied Thorndyke. “I think that if the superintendent will take this key to Hanover Buildings, Dockhead, Bermondsey, he may possibly find a door that it will fit.”

“The deuce!” exclaimed Miller. “I beg your pardon, madam; but I thought I had gone through that coat pretty completely. What was it that I had overlooked, sir? Was there a letter hidden in it, after all?”

“You overlooked the dust on it, Miller; that is all,” said Thorndyke.

“Dust!” exclaimed the detective, staring round-eyed at my colleague. Then he chuckled softly. “Well,” said he, “as I said before, I’m not a sorcerer; I’m only a policeman.” He picked up the key and asked: “Are you coming to see the end of it, sir?”

“Of course he is coming,” said Mrs. Chater, “and Dr. Jervis too, to identify the man. Now that we have gotten the villain we must leave him no loophole for escape.”

Thorndyke smiled dryly. “We will come if you wish it, Mrs. Chater,” he said, “but you mustn’t look upon our quest as a certainty. We may have made an entire miscalculation, and I am, in fact, rather curious to see if the result works out correctly. But even if we run the man to earth, I don’t see that you have much evidence against him. The most that you can prove is that he was at the house and that he left hurriedly.”

Mrs. Chater regarded my colleague for a moment in scornful silence, and then, gathering up her skirts, stalked out of the room. If there is one thing that the average woman detests more than another, it is an entirely reasonable man.

The big car whirled us rapidly over Blackfriars Bridge into the region of the Borough, whence we presently turned down Tooley Street towards Bermondsey.

As soon as Dockhead came into view, the detective, Thorndyke and I, alighted and proceeded on foot, leaving our client, who was now closely veiled, to follow at a little distance in the car. Opposite the head of St. Saviour’s Dock, Thorndyke halted and, looking over the wall, drew my attention to the snowy powder that had lodged on every projection on the backs of the tall buildings and on the decks of the barges that were loading with the flour and ground rice. Then, crossing the road, he pointed to the wooden lantern above the roof of the spice works, the louvres of which were covered with greyish-buff dust.