In June 1916, a young woman named Charlotte Reid is found murdered in a cinema. Harvery Marmion and Joe Keedy are assigned the task of finding the killer who so elusively fled in the dark. Before long, two more victims, of striking similarity but differing backgrounds, are found dead around the city. Meanwhile, miles from home, Marmion's son Paul prepares for life on the front line as he marches towards the Battle of the Somme.