The Secret Adversary is a work of detective fiction by Agatha Christie 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 book introduces the characters of Tommy and Tuppence who feature in three other Christie novels and one collection of short stories; the five Tommy and Tuppence books span Agatha Christie's writing career.