Armstrong examines the drink and finds it was poisoned, but since Marston poured it himself, the guests assume he committed suicide. Still, they find it hard to believe that such a high-spirited young man would want to take his own life. Marston’s body is carried to his bedroom and placed beneath a sheet. After a time, everyone goes upstairs to bed except for Rogers, who stays downstairs to clean up. As they enter their rooms, each guest locks his or her door. The house, so modern and gleaming, now seems horrifying in its blankness.
As he prepares for bed, Wargrave thinks about Edward Seton, the man whom the voice earlier accused him of sentencing to death. The defense defended Seton well, and the prosecution presented a poor case. Everyone assumed the jury would acquit Seton. Wargrave smiles, remembering how during his summing up “[h]e’d cooked Seton’s goose.” Downstairs, Rogers notices that although ten little Indian statues originally sat on the table, now there are only nine. Macarthur lies awake in bed, recalling how during World War I he discovered that his young wife was having an affair with one of his officers. Furious, he ordered the officer, Richmond, on an impossible mission, effectively sending him to his death. No one suspected him at the time, except perhaps one of the other officers, a man named Armitage. His wife became distant and died of pneumonia a few years later. Macarthur retired and lived by the sea, but after a time he began to worry, suspecting that Armitage had spread the story around and that people knew his secret. Now, lying in his bedroom listening to the sound of the sea, a strange feeling of peace comes over him, and he realizes that he does not really want to leave the island.
In her bedroom, Vera remembers her time as Cyril’s governess. She was in love with Cyril Hamilton’s cousin, Hugo, but Hugo was too poor to marry her and support both himself and her. Vera knew that if Cyril died, Hugo would inherit the family fortune. One day Cyril begged her again and again to be allowed to swim to a rock in the ocean. Vera pushes these recollections aside. As she passes the mantelpiece, she notices the similarity between Marston’s death and the first verse of the “Ten Little Indians” poem, which reads, “One choked his little self and then there were nine.”
Armstrong has a nightmare in which he stands at his operating table, realizing he must kill the patient on the table. The patient looks like Emily Brent, then like Marston. Rogers, worried because he cannot rouse his wife, comes into the room and wakes Armstrong. Armstrong rises and goes to find that Mrs. Rogers has died in her sleep, perhaps of an overdose of sleeping pills. Rogers says she took only the pills Armstrong gave her.
In the morning the guests rise, hoping to catch sight of the boat back to the mainland. Vera, Lombard, and Blore go to the summit of the island to watch for it, but it doesn’t appear. After breakfast, Armstrong announces Mrs. Rogers’s death to the group. The group is alarmed, and Macarthur gives Rogers his condolences when he returns to the room. When Rogers leaves the room, the group begins to speculate about the cause of his wife’s death. Emily Brent insists it was an act of God and that Mrs. Rogers died of a guilty conscience after hearing the recorded accusation of murder the previous night. Blore suggests that Rogers killed his wife in the hopes of covering up their secret.
After the meal, Blore and Lombard discuss their situation on the terrace and decide that the boat will not come. Macarthur, passing them, expresses his agreement in a dazed voice and wanders off, saying that none of them will ever leave the island. Meanwhile, a baffled and frightened Rogers shows Armstrong that only eight Indian figures remain on the table.