This letter ostensibly came from a firm of estate agents in the Harrow Road. I made an immediate inquiry, and was not altogether surprised to learn that no such a firm existed. In the meantime I studied the letter on the assumption that it contained a spy cipher, and after some hours' work succeeded in extracting from its apparently innocent contents the following startling message: "_Angorania_ will convey troops from Montreal on 30th proximo." This set me at work with furious speed. An inquiry at the port offices showed me that the great liner was at the moment lying at Avonmouth, and that she would sail for Montreal a week later in order to bring over several thousand Canadian troops. Shackleton now made what was to me, I confess, a very welcome return to the scene. I had been seriously perturbed by the fear that we had lost him. While he was under my own immediate observation I felt capable of checkmating his designs, but the knowledge that an able enemy agent was at large and uncontrolled, with enough herbethite in his possession to create an appalling disaster, worried me more than I can tell. Shackleton appeared on the scene the day after the delivery of the letter we had intercepted and photographed. Where he had been in the interval we never learned, but he did not arrive in Bristol from London; that was certain, for every train, day and night, was closely watched. Evidently the letter meant a good deal to him. He went at once to Avonmouth, closely followed by Moore. To our intense surprise, he seemed very well known at the docks and was freely admitted everywhere. He walked along the quays for some time, and we noted his obvious interest in the _Angorania_, now busily getting ready for her coming trip. We learned later that Shackleton had very cleverly wound himself into the confidence of a local shipping agent, and by this means had secured such frequent admission to the docks that his presence there was accepted almost as a matter of course. I now began to feel practically certain that the _Angorania_ was the object of the conspirators, and that the herbethite was the means to be adopted to bring about her destruction. But how? Madame Gabrielle was to solve the question for us. The great liner was timed to leave at six o'clock, and an hour earlier the boat-train had arrived from London, bringing an unusually large assembly of passengers. These included several Government officials on their way to Canada, a number of highly placed military officers, and the members of two or three important war commissions. Some time after the arrival of the train, a shabbily-dressed woman in a battered old hat pushed rudely against me. I turned, and to my amazement recognised Madame Gabrielle. She was obviously almost at the end of her strength, pallid with fatigue, and with deep circles round her eyes which spoke eloquently of exhaustion.