The Big Four is a mystery novel by Agatha Christie, first published in the UK by William Collins & Sons on 27 January 1927 and in the US by Dodd, Mead and Company later in the same year. It features Hercule Poirot, Arthur Hastings, and Inspector Japp. The UK edition retailed at seven shillings and sixpence (7/6) and the US edition at $2.00.