Although he was once an established detective, the selfish and careless William Blore is woefully unprepared for his supposed mission on Soldier Island. His invitation to the island implies that one of the guests might try to steal Mrs. Owen’s jewels, so he has been hired to discreetly keep them safe. Blore opts to go undercover as a man named Davis from South Africa, as he recently read a travel pamphlet on that country. Upon arriving on the island, he and the other guests quickly realize there is no Mrs. Owen, there are no jewels, and Davis is a ruse that cannot stand up to scrutiny. It is the record that initially reveals Blore’s true identity, but Lombard says he knew Blore was lying even before the record confirms it.

As the characters attempt to solve their conundrum, either by finding the murderer or getting off the island, Blore largely lets others offer potential theories and solutions. He steps in to help Lombard and Armstrong search the island for Mr. Owen but does not initially suggest it himself. Instead of seeking solutions, Blore vocalizes his suspicions about multiple characters, adding to the tension in the house early in the novel. The death Blore is accused of causing is that of James Stephen Landor. Blore later reveals he testified against Landor to gain a promotion for himself, even though Landor was innocent. This piece of information lets the reader know they cannot fully trust Blore’s instinct about who might be guilty.

Blore survives almost to the end of the novel, with only Lombard and Vera left after him. The note at the end of the novel explains that the victims were chosen in order of how guilty the murderer perceived them to be. Blore, then, is forced to suffer longer than some of the other characters because he knew Landor was innocent when Blore incriminated him. The murderer expresses disdain for anyone who causes the deaths of innocent people. The murderer sees Blore’s action as a particularly horribly miscarriage of justice because Blore’s testimony was deliberately false. He knew Landor was innocent and sent him to his death anyway.