In Agatha Christie's And Then There Were None, eight strangers are brought to an island off the coast of Devon by a mysterious man name U. N. Own, where they are each revealed to have caused the deaths of various people in their lives. One by one, the strangers are killed off in a different number of ways: the poisoning of Tony Marston, the overdose of Ethel Rogers, etc.
When Blore, Lombard, and Armstrong go off in search of the lunatic on the island, they end up failing to locate any suspects. Everyone eventually dies, and the police arrive to discover the bodies littering the island. The mastermind behind this plan is then revealed to be Justice Margrave, one of the initial strangers, who brought the victims to the island to punish them for their sins.
Blore, Lombard, and Armstrong search the island from top to bottom in search of the murderer. Unfortunately for them, they find absolutely nothing. They disocver that they are completely alone on the island and the only possibility is that one of the remaining guests is the murderer. This is an important part of the novel, because it's the moment when we realize that the situation is utterly hopeless. There isn't anyone coming to help and the murderer is playing off of everyone's fear. Some may consider this the climax or turning point of the novel since it is a scene of maximum intensity.