DI Walter Gambon is a self-styled “Yoda of the force”, whose workload suddenly increases when he’s handed the cases of an officer who committed suicide by throwing himself under a Tube train. Or was he pushed? Gambon must work out whether his former colleague was murdered, while tracking down another officer who has gone so far undercover that nobody knows where he (or she) is.

Martin's comfortable world is upturned by his friend's mid-life crises, beginning with his best friend's suicide, and the secret affair he had with Martin's wife.