The Bacteriologist has a visitor to his laboratory, a pale stranger who arrives with a letter of introduction from a good friend of the scientist. The scientist shows his visitor the cholera bacillus under a microscope and they talk about the disease. The visitor is particularly interested in a vial containing living bacteria, and the scientist describes the power of cholera, saying what a terrible epidemic could be caused if a tube such as the one he holds were to be opened into the water supply.The scientist's wife calls him away for a moment; when the scientist returns, the visitor is ready to leave. As soon as the visitor has gone, however, the scientist realizes the vial of bacteria is missing, that the visitor must have stolen it. He runs out in a panic, sees the visitor's cab leaving, and hails another cab to give chase. The scientist's wife, horrified by his inappropriate dress and hurry, follows in a third cab, with her husband's shoes and coat and hat.We shift to the point of view of the visitor in his cab. He has indeed stolen the vial. He is an Anarchist who plans to release the bacteria into London's water supply. His motivation is fame: he feels he has been neglected by the world, and now he will reveal his power and importance. In the speeding cab, however, he accidentally breaks the glass vial.He decides to become a human vector. He swallows what is left in the vial, and stops the cab, realizing that he no longer needs to flee. When the scientist catches up and confronts him, the Anarchist gleefully announces what he has done. The scientist allows him to walk away, and tells his wife that the man has ingested the stolen bacteria.There is a twist: the vial, it turns out, did not contain cholera, but a strange newmicrobe the Bacteriologist had been studying, the only known effect of which is to make the skin of the animals exposed to it turn bright blue. The Bacteriologist reluctantly puts on his coat and returns home with his wife, complaining that he will now have to culture the bacillus all over again.