The Secret Adversary is a work of detective fiction by Agatha Christie and first published in the United Kingdom by The Bodley Head in January 1922 and in the United States by Dodd, Mead and Company later in that same year. The UK edition retailed at seven shillings and sixpence (7/6) and the US edition at $1.75. The book introduces the characters of Tommy and Tuppence who feature in three other Christie books and one collection of short stories written throughout her writing career.