The Secret Adversary is the second published detective fiction novel by British writer Agatha Christie, first published in January 1922 in the United Kingdom by John Lane at The Bodley Head 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 novels and one collection of short stories; the five Tommy and Tuppence books span Agatha Christie's writing career. They are hired for a job that leads them both to many dangerous situations, meeting allies as well, including an American millionaire in search of his cousin. Reviews were generally positive on this adventure, which manages to keep the identity of the arch-criminal secret to the very end.