If famed crime novelist Agatha Christie knows one thing, it's how to draw her listeners in with a series of subplots and converging story lines. The Secret Adversary, which is the first novel in the series that follows Tommy and Tuppence, chronicles the pair's quest to find a mysterious woman who goes by the name of Jane Finn. Earlier in 1915, Jane Finn had been given a secret document while aboard the Lusitania, which was sunk due to a torpedo hit. That document was a treaty, and Jane was entrusted by the stranger who gave it to her to deliver it to the American Embassy located in London. Years later, the document has still never been delivered, and there's no word as to who Jane Finn is, nor where she is.

Tommy and Tuppence, upon meeting for the first time, decide that they're going to establish a sort of business in which they embark on adventures. They begin to work with a man named Mr. Carter who tells them that the clock is ticking in England - thanks to the labor unrest that the country is experiencing - and that one of the prominent figures behind this upheaval is a Mr. Brown. Together, Tommy and Tuppence seek to find Mr. Brown, discover the truth about Jane Finn, and help England by tracking down that treaty.