Angels in the gloom

March 1916: Joseph Reavley, stumbling across the wastes of no-man's-land to rescue a comrade, is badly wounded and sent home on sick leave. He is cared for by his sister Hannah, who is anxious about her husband, Archie, away at sea. Hannah and Joseph are delighted when Shanley Corcoran, an old friend, comes to visit. Corcoran confides in Joseph that he's close to completing an invention that will paralyse the German U-boats. But soon afterwards, a scientist is found murdered, and it's evident that secrets have been betrayed to the enemy. Joseph's brother Matthew, of the S.I.S., comes to investigate, and together the men embark on a search that will solve the crime and lead them to the spy.