"Naturally you want to know what this has to do with the Thames," Darbyshire observed. "I'm going to tell you. The Santa Anna was deliberately wrecked for a purpose which you will see later. The crew for the most part landed not far away and, for reasons of their own, sank their boat. It isn't far from Aldenburgh to London: in a short time the Portuguese were in the Metropolis. Two or three of them remained there, and five of them proceeded to tramp to Ashchurch, which is on the river, and not far from Oxford. Being short of money, their idea was to tramp across to Cardiff and get a ship there. Being equally short of our language, they get out of their way to Ashchurch. Then three of them are taken ill, and two of them die. The local practitioner sends for the medical officer of health. The latter gets frightened and sends for me. I have just got back. Look here." Darbyshire produced a phial of cloudy fluid, some of which he proceeded to lay on the glass of a powerful microscope. Longdale fairly staggered back from the eyepiece. "Bubonic! The water reeks with the bacillus! I haven't seen it so strongly marked since we were in New Orleans together. Darbyshire, you don't mean to say that this sample came from----" "The Thames? But I do. Ashchurch drains directly into the river. And for some few days those sailors have been suffering from a gross form of bubonic fever. Now you see why they ran the Santa Anna ashore and deserted her. One of the crew died of plague, and the rest abandoned her. We won't go into the hideous selfishness of it; it was a case of the devil take the hindmost." "It's an awful thing," Longdale groaned. "Frightful," Darbyshire murmured. He was vaguely experimenting with some white precipitate on a little water taken from the phial. He placed a small electric battery on the table. "The great bulk of the London water supply comes from the Thames. Speaking from memory, only the New River and one other company draw their supply from the Lea. If the supply were cut off, places like Hoxton and Haggerstone and Battersea, in fact all the dense centres of population where disease is held in on the slenderest of threads, would suffer fearfully. And there is that deadly poison spreading and spreading, hourly drawing nearer to the metropolis into which presently it will be ladled by the million gallons. People will wash in it, drink it. Mayfair will take its chance with Whitechapel." "At any hazard the supply must be cut off!" Longdale cried. "And deprive four-fifths of London of water altogether!" Darbyshire said grimly. "And London grilling like a furnace! No flushing of sewers, no watering of roads, not even a drop to drink. In two days London would be a reeking, seething hell--try and picture it, Longdale." "I have, often," Longdale said gloomily. "Sooner or later it had to come. Now is your chance, Darbyshire--that process of sterilisation of yours."