"Zena from the first suggested that we must find Frederick Ewing," said Quarles; "and her intuition was right. We know--at least I think we may take it as an established fact--that a very expert gang has been at work in London during the past few months, and it was reasonable to assume that this robbery was their work, with the help of someone connected with the bank. Practically speaking, it would have been impossible without inside and absolutely accurate information. A process of elimination left Ewing as the likely person to give this help. We need not go over all the difficulties the gang would have to contend with; they were many, not the least being the successful removal of the spoil; but I asked myself whether this gang was not a sort of obsession with us, whether the robbery might not have been a one-man job. You will remember I questioned the general manager on the possibility of Ewing being alone in the strong-rooms, and whether the gold might not have been removed by degrees. He laughed at the idea, but ridicule never yet made me give up a theory. I looked for something to support my theory, and I found many things. The action of the explosive had been peculiar. The manner of the damage was not quite what one would have expected from gelignite, or some equally powerful preparation. Further, why was Coulsdon found in the outer safe? It is reasonable to suppose that he was rendered insensible before the explosion took place, or he might have heard it. Why, then, should he be dragged into the safe? A gang would not have troubled to do this, but, if the job were a one-man affair, the thief might reasonably want to keep his eye upon the porter in case he should recover consciousness. Now, to come back to the explosion, it seemed to me that so far as the door of the inner strong-room was concerned it had not been locked, at any rate not fully locked, when the explosion took place. Was there any support to this theory to be found? Yes. I will show you presently the debris I picked out of the lock. It contains portions--small, but quite recognizable--of a key, not polished, as would be the case if used constantly, but rough. This suggested that duplicate keys had been made. That key, Wigan, I believe, was in the lock when the explosion took place. It was blown to pieces by the explosion, but the burglar must have discovered his mistake, and gathered up the pieces, for I could discover nothing either on the strong-room floor or in the passage without. I found another support to my theory in the window on the roof. Someone had got out as well as in--got out, Wigan, to hide, and got in again when the moment for action had come." "But----"