The Secret Adversary (Unabridged‪)‬

It is just after World War I and Tommy Beresford and Tuppence Cowley are desperately short of money. With jobs on thin ice and restless for excitement, they embark on a daring business scheme - Young Adventurers Ltd. 'willing to do anything, go anywhere'. When their first assignment, for the sinister Mr. Whittington, puts both of them in mortal danger, they have to use all of their ingenuity and cunning to save not only their own lives, but that of the mysterious Jane Finn.