Secret Adversary

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. The Great War is over, and jobs are scarce. Childhood friends Tommy Beresford and Prudence "e;Tuppence"e; Cowley meet and agree to start their own business as The Young Adventurers. 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. (Wikipedia)