"The Secret Adversary" by Agatha Christie is a detective novel published in January 1922. Two unemployed young friends, Tommy and Tuppence, form a business seeking adventure and quickly find themselves entangled in a dangerous conspiracy involving a missing woman, a secret treaty from the Lusitania, and a mysterious criminal mastermind known only as "Mr. Brown." Their investigation leads them through deception, kidnapping, and betrayal as they race to recover the treaty before it destabilizes the British government.