Eight people, all strangers to each other, are invited to Indian Island, off the English coast. Vera Claythorne, a former governess, thinks she has been hired as a secretary; Philip Lombard, an adventurer, and William Blore, an ex-detective, think they have been hired to look out for trouble over the weekend; Dr. Armstrong thinks he has been hired to look after the wife of the island’s owner. Emily Brent, General Macarthur, Tony Marston, and Judge Wargrave think they are going to visit old friends.
When they arrive on the island, the guests are greeted by Mr. and Mrs. Rogers, the butler and housekeeper, who report that the host, someone they call Mr. Owen, will not arrive until the next day. That evening, as all the guests gather in the drawing room after an excellent dinner, they hear a recorded voice accusing each of them of a specific murder committed in the past and never uncovered. They compare notes and realize that none of them, including the servants, knows “Mr. Owen,” which suggests that they were brought here according to someone’s strange plan.
As they discuss what to do, Tony Marston chokes on poisoned whiskey and dies. Frightened, the party retreats to bed, where almost everyone is plagued by guilt and memories of their crimes. Vera Claythorne notices the similarity between the death of Marston and the first verse of a nursery rhyme, “Ten Little Indians,” that hangs in each bedroom.
The next morning the guests find that Mrs. Rogers apparently died in her sleep. The guests hope to leave that morning, but the boat that regularly delivers supplies to the island does not show up. Blore, Lombard, and Armstrong decide that the deaths must have been murders and determine to scour the island in search of the mysterious Mr. Owen. They find no one, however. Meanwhile, the oldest guest, General Macarthur, feels sure he is going to die and goes to look out at the ocean. Before lunch, Dr. Armstrong finds the general dead of a blow to the head.
The remaining guests meet to discuss their situation. They decide that one of them must be the killer. Many make vague accusations, but Judge Wargrave reminds them that the existing evidence suggests any of them could be the killer. Afternoon and dinner pass restlessly, and everyone goes to bed, locking his or her door before doing so. The next morning, they find that Rogers has been killed while chopping wood in preparation for breakfast. At this point, the guests feel sure the murders are being carried out according to the dictates of the nursery rhyme. Also, they realize that the dining-room table initially featured ten Indian figures, but with each death one of the figures disappears.
After breakfast, Emily Brent feels slightly giddy, and she remains alone at the table for a while. She is soon found dead, her neck having been injected with poison. At this point, Wargrave initiates an organized search of everyone’s belongings, and anything that could be used as a weapon is locked away. The remaining guests sit together, passing time and casting suspicious looks at each other. Finally, Vera goes to take a bath, but she is startled by a piece of seaweed hanging from her ceiling and cries out. Blore, Lombard, and Armstrong run to help her, only to return downstairs to find Wargrave draped in a curtain that resembles courtroom robes and bearing a red mark on his forehead. Armstrong examines the body and reports that Wargrave has been shot in the head.
That night, Blore hears footsteps in the hall; upon checking, he finds that Armstrong is not in his room. Blore and Lombard search for Armstrong, but they cannot find him anywhere in the house or on the island. When they return from searching, they discover another Indian figure missing from the table.
Vera, Lombard, and Blore go outside, resolving to stay in the safety of the open land. Blore decides to go back into the house to get food. The other two hear a crash, and they find someone has pushed a statue out of a second-story window, killing Blore as he approached the house. Vera and Lombard retreat to the shore, where they find Armstrong’s drowned body on the beach. Convinced that Lombard is the killer, Vera steals Lombard’s gun and shoots him. She returns to her bedroom to rest, happy to have survived. But upon finding a noose waiting for her in her room, she feels a strange compulsion to enact the last line of the nursery rhyme, and hangs herself.
The mystery baffles the police until a manuscript in a bottle is found. The late Judge Wargrave wrote the manuscript explaining that he planned the murders because he wanted to punish those whose crimes are not punishable under law. Wargrave frankly admits to his own lust for blood and pleasure in seeing the guilty punished. When a doctor told Wargrave he was dying, he decided to die in a blaze, instead of letting his life trickle away. He discusses how he chose his victims and how he did away with Marston, Mr. and Mrs. Rogers, Macarthur, and Emily Brent. Wargrave then describes how he tricked Dr. Armstrong into helping him fake his own death, promising to meet the doctor by the cliffs to discuss a plan. When Armstrong arrived, Wargrave pushed him over the edge into the sea, then returned to the house and pretended to be dead. His ruse enabled him to dispose of the rest of the guests without drawing their suspicion. Once Vera hanged herself on a noose that he prepared for her, Wargrave planned to shoot himself in such a way that his body would fall onto the bed as if it had been laid there. Thus, he hoped, the police would find ten dead bodies on an empty island.