The Secret Adversary by Agatha Christie
Out of luck and out of money, childhood friends Tommy Beresford and Tuppence Cowley re-meet in London and decide to join forces to become “The Young Adventurers, Ltd.,” planning to hire themselves out as adventurers. Overheard plotting their adventure, Tuppence is almost immediately offered a job, only to be accused of blackmail when she gives her name as “Jane Finn,” not realizing it was a name she had overheard earlier. Jane Finn, it seems, is a young American woman who disappeared after surviving the sinking of the RMS Lusitania, where she was entrusted with important documents by a man who worried that he wouldn’t be able to get on a lifeboat. Further complicating matters are a secret conspiracy, another detective, and Jane’s rich American cousin, who has come to England looking for her.
Christie relies a lot on coincidence and clichés, but deliberately so. My understanding is that the “Tommy & Tuppence” stories are often largely comprised of Christie deliberately using the clichés of the mystery genre as having Tommy and Tuppence mimic famous detectives. Whatever it is that she’s trying for, it works, and the book is a very enjoyable romp. I think Tommy ends up more the detective than Tuppence does, but Tuppence is a bit more of an adventuress, and is the main driving force of the venture, and I’m particularly fond of how she’s absolutely shameless about wanting and needing money, and being willing to marry for it, rather than being nobly destitute.