The series revolves around the cases of Inspector Ian Rutledge, a veteran of the First World War who has returned to the police force (Scotland Yard) as a detective, but is battling with post-traumatic stress disorder.
He must hide this information from those around him in order to avoid the social stigma which accompanied psychological, mental, or emotional issues in the early 20th century.
Rutledge is then unexpectedly buried alive with the man's corpse when an artillery shell explodes in the camp.
The existence of Hamish's voice is a secret Rutledge must keep from everyone, especially his jealous Scotland Yard superior who wants to see him removed, all while solving murders.
When Rutledge returns from the Western front in 1919 he is treated in a hospital for his various symptoms only to be left by his fiancée, Jean.