Just after World War One, Tommy Beresford and Tuppence Cowley are desperately short of money. With jobs thin on the ground they decide to form a partnership, hiring themselves out as 'young adventurers, willing to do anything, go anywhere'. In their first dangerous assignment, they must use all their ingenuity to save not only their lives but also the life of the mysterious 'Jane'.

Christie was inspired to write The Secret Adversary after overhearing a conversation in a cafe. Two women were discussing a lady called Jane Fish, which struck Christie as a most 'entertaining' name, and she soon began work on a new novel. Originally titled The Joyful Venture, the name changed to The Young Adventurers before finally becoming The Secret Adversary.

The woman's name that inspired Christie would change from Jane Fish, to Jane Finn. It was the second novel Christie wrote and the first to star Tommy and Tuppence. Published in 1922, it became the first novel to be made into a film; Fox Film in Germany adapted it under the title 'Die Abenteuer G.m.b.H. It was adapted in the UK in 1985 and starred Francesca Annis and James Warwick as Tommy and Tuppence. It was later shown in the USA on PBS.