When Simon Bowles commits suicide, no one is surprised. A graduate student in mathematics at Cambridge University, Bowles had a long, well-documented history of depression. But as Detective Sergeant Derek Smailes soon discovers, he also had a passion for investigating historical mysteries and an extraordinary knack for solving them. His most recent project: uncovering the identity of the fabled fifth man in the notorious Cambridge spy-ring of the 1930s. Could Bowles possibly have solved that mystery? And could his solution?his theorem?have brought about his death? Rooted in the (thoroughly researched) history of the Cambridge Spies.