When Gerry Wade sleeps in and is late for breakfast, his friends find that he has a very good reason - he's been murdered. Lady Eileen Brent, known to her friends as Bundle and in whose bed Wade died, returns home and decides to investigate. When a second man is killed, he mentions something about " ...seven dials...tell Jimmy Thesiger..." but Thesiger has no idea what he was talking about. What they learn is of the existence of a secret society and of a hugely valuable formula for making a specialized form of steel. But who exactly is behind the two murders and why were they killed?

Childhood friends Tommy and Tuppence meet in London after having served in World War I. Recently "demobed", short of money, and with no job prospects, they decide to become adventurers for hire. Soon, they are employed by the British Government to locate a secret treaty signed before the war.