Tommy Beresford meets Prudence Cowley, also known as Tuppence, after the First World War. Seeking work, they team up and call themselves 'The Young Adventurers'. Fairly soon adventurous work involving a smuggled international treaty comes their way, and they are plunged into a world of crime and intrigue while they search for a mysterious woman known only as 'Jane Finn' and an arch criminal who calls himself Mr. Brown.