In June 1916, a young woman is found murdered in a cinema. Harvery Marmion and Joe Keedy set out to find 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. Suffering a vicious blow in No Man's Land, Paul is left blinded for the rest of his life. Marmion must come to terms with the permanent darkness of his son's life, while continuing to search for the brutal killer who only strikes in the dark.