On the way to Apia in the Pacific, a ship stops at Pago Pago. The passengers include Dr Macphail and his wife, and Davidson, a missionary, and his wife. (The story is seen from Macphail's point of view.) Because of an epidemic of measles (a serious disease for local people) on the island, the ship cannot leave until it is sure none of the crew is infected. The Macphails and the Davidson's find lodgings with Horn, a trader on the front. For most of their stay there is heavy rain which they find oppressive. Macphail hears from the missionary and his wife about the severity of Davidson in his work. Also staying there from the ship is Miss Thompson. From her room is the sound of a gramophone and men's voices. They remember she came on board at Honolulu and is presumably from Iwelei, the red-light district there. Davidson is determined to stop her activities and tries to get Horn to stop her having visitors. Macphail feels that Davidson is "mysteriously at work. He had an impression that he was weaving a net around the woman, carefully, systematically, and suddenly, when everything was ready would pull the strings tight." Davidson sees the governor of the island and gets him to put Miss Thompson on the next ship, which goes to San Francisco. The governor, aware that the missionaries have influence, does not change his decision when Macphail visits him. Miss Thompson is distraught, as she will be sent to the penitentiary if she returns to San Francisco. Davidson is often with Miss Thompson, whom he now knows as Sadie; her personality changes and she becomes repentant, it appears. Davidson says to the Macphails, "It's a true rebirth. Her soul, which was black as night, is now pure and white.... All day I pray with her...." A few days later Davidson's body is found on the beach; he has cut his throat with a razor. Macphail does not understand what happened until, returning to his lodgings, he finds Sadie Thompson has changed suddenly back to "the flaunting quean they had known at first"; she breaks into "a loud, jeering laugh" at Mrs Davidson and the Macphails, and says to Macphail, "You men! You filthy, dirty pigs! You're all the same, all of you."