Third Girl (Hercule Poirot, #40)

Three young women share a London flat. The first is a coolly efficient secretary. The second is an artist. The third isn't as easy to pin down. One day she visits Hercule Poirot unexpectedly while he's having breakfast and confesses that she is a murderer—and then promptly disappears. Slowly, Poirot learns of the rumours surrounding the mysterious third girl, her family, and her disappearance. Yet hard evidence is needed before the great detective can pronounce her guilty, innocent, or insane.