Spoiler Alert!
All the characters, invited to Soldier Island by a mysterious host, are systematically murdered, each death echoing a verse from the children's rhyme "Ten Little Indians." The final two survivors, Vera Claythorne and Philip Lombard, believe they have escaped the killer only to discover the killer was none other than themselves.
They had been the ones responsible for the deaths of others, and in a twisted sense of justice, they each decided to end their own lives.
The ending leaves the reader with a sense of despair and the chilling realization that even the most cunning and seemingly innocent can harbor dark secrets and be capable of great evil.