It is 1921 and a terrible discovery has been made at a manor house in Upton Hanger in Surrey - the bloodied bodies of Colonel Fletcher, his wife and two of their staff. The victims have all been stabbed - and the lack of disturbance in the house suggests the attack was one of terrifying speed.
The Surrey police force seem ready to put the murders down to robbery with violence, but Detective Inspector Madden, from Scotland Yard, sees things slightly differently. For he has experienced the horrors of World War I and has seen madness at first hand. And this crime he is sure has been perpetrated by a psychopath who will strike again ... and soon.