The weapon was at her head when the villain dropped, and I have sometimes thought that, whatever his intention the moment before, in the act of pressing the trigger the professor realized that only the man's death could save the woman. It was hot work for a moment. The man who had burst open the door got a nasty knife thrust, and I had been obliged to fire at my assailant before our comrades rushed to our aid. There is no enemy more dangerous than a man armed with a knife when he knows how to use it, and when the space to fight in is so confined that to use firearms is to endanger your friends. Indeed, I thought the woman had been shot, but she had only fainted, although it was quite impossible to question her fully until next day. "Those papers may be useful," said Quarles, when our captives had been taken to the police station, pointing to the documents which had fallen from a little table pushed aside in the struggle. "The ends of a big affair are in our hands, I fancy, and, with the help of Mrs. Fitzroy, we may get several more dangerous fanatics under lock and key." Late that night I was with the professor in Chelsea. He had gone straight home from Hambledon Road, and, after a visit to the police station and a long consultation with Scotland Yard over the 'phone, I followed him. There were several questions I wanted to ask, for his handling of this affair seemed to me so near to the marvelous that I wondered whether he had had some knowledge of this gang before we had heard of the house in Kew. "No, Wigan, no," he said, in reply to my question. "I did not even know there was such a place as Hambledon Road." "I am altogether astonished." "And not for the first time, eh, Wigan? Yet this case has been worked upon facts chiefly. It was clear that the idea of the woman going suddenly to the telephone to call for help was absurd, and, therefore, it was at least possible that she had spoken that message under compulsion. When the revolver was held to her head in the cellar to-night, it was probably not for the first time. As I said this morning, there was a desire to put the authorities on the scent. This suggested a conspiracy. So much for theory, now for facts." "But we did not know murder had been committed then," I said. "Mrs. Fitzroy said so in her message," Quarles answered, "and it was unlikely the police would have been called unless they were meant to discover something. But we had facts to go upon. It was evident that two persons had sat by the fire, the position of the chairs, the cigar ash on the hearth----" "Cigarette, you mean."