Three Act Tragedy is a work of detective fiction by Agatha Christie and first published in the US by Dodd, Mead and Company in 1934 under the title of Murder in Three Acts and in UK by the Collins Crime Club in January 1935 under Christie's original title. The US edition retailed at $2.00 and the UK edition at seven shillings and sixpence (7/6).
The book features Hercule Poirot and Mr. Satterthwaite. This is the one book in which Satterthwaite collaborates with Poirot. He previously appeared in the stories which feature Mr. Harley Quin, in particular those collected in The Mysterious Mr. Quin (1930).