Dr. Armstrong . . . raised the wig. It fell to the floor, revealing the high bald forehead with, in the very middle, a round stained mark from which something had trickled . . . Dr. Armstrong . . . said—and his voice was expressionless, dead, far away: “He’s been shot.”
This passage comes from the end of Chapter XIII, when the group of guests finds what appears to be the corpse of Judge Wargrave. In fact, only Dr. Armstrong examines the body, and only he declares that Wargrave has died from a shot to the head. We discover later that Armstrong has agreed to help Wargrave fake his own death, going along with the ruse because he does not suspect Wargrave of being the killer. The conspiracy gives Wargrave a free hand, since no one but Armstrong knows that he is alive. As long as no one sees him, Wargrave can do as he pleases and no one will suspect him.
There is little to help us deduce that Wargrave is not actually dead. We share the perception of the remaining guests, who assume that Wargrave has died and has thus been eliminated as a suspect. By not telling us exactly what transpires, Christie breaks the rules of the traditional detective story, in which the reader can, theoretically, examine the clues and solve the mystery. This rule-breaking dramatically increases the novel’s suspense, since, with Wargrave’s faked death, subsequent events seem inexplicable and almost supernatural.