The Secret Adversary (Illustrated)

In the Prologue, a man aboard the RMS Lusitania on 7 May 1915 quietly gives important papers to a young American woman, as she is more likely to survive the sinking ship.
In 1919 London, demobilised soldier Tommy Beresford meets war volunteer Prudence "Tuppence" Cowley, both out of work and money. They form the "The Young Adventurers, Ltd", planning to hire themselves out with "[n]o unreasonable offer refused."