Agatha Christie: Third Girl

Third Girl is a work of detective fiction by Agatha Christie and first published in the UK by the Collins Crime Club in November 1966 and in the US by Dodd, Mead and Company the following year.
It features her Belgian detective Hercule Poirot and the recurring character Ariadne Oliver. The novel is notable for being the first in many years in which Poirot is present from beginning to end. It is uncommon in that the investigation includes discovering the first crime, which happens comparatively late in the novel.