Soho during the blackouts of the Second World War. When a piercing scream rends the air and a bloodied knife is found, Detective Inspector MacCarthy is soon on the scene. He must move through the dark, seedy Soho underworld - peopled by Italian gangsters, cross-dressing German spies and glamorous Austrian aristocrats - as he attempts to unravel the connection between the mysterious Madame Rohner and the theft of secret anti-aircraft defence plans.