London in the aftermath of the First World War is full of demobilised soldiers and idle young people with no money and no prospects. Tommy Beresford and Prudence "Tuppence" Cowley, childhood friends who meet again by chance, find themselves in exactly that position, and in a fit of bravado they decide to hire themselves out for any job, however dangerous, under the name "the Young Adventurers." Their advertisement draws them almost at once into something far larger than they imagined. A chance-overheard name, Jane Finn, turns out to belong to a young American woman who vanished years earlier while carrying a secret government treaty entrusted to her aboard a sinking ship. Recruited by a shadowy official, the pair set out to trace Jane Finn and recover the document before it can be used to bring down the British government. Standing against them is a criminal mastermind known only as Mr Brown, whose true identity no one has ever discovered and whose reach extends into the highest circles. With the help of a wealthy American searching for his missing cousin, Tommy and Tuppence follow a trail of false identities, kidnappings and double-crosses through drawing rooms and back streets. Lightly comic in tone yet steadily tense, this early adventure pairs amateur sleuthing with espionage, testing the courage and loyalty of two ordinary people who refuse to be frightened off.