Ramon (Francis DeWolff) is the Armenian merchant who lives in his mansion outside of London. He has augmented his income over the years by blackmailing his clients. Fearful of retribution, he installs a room in his mansion that is supposedly impenetrable, complete with a hotline to Scotland Yard in the event of a break-in. One by one, Ramon's friends and associates are murdered, as the trail of blood oozes closer to his door. Scotland Yard sends out special agent Meredith (Bernard Lee) at the request of the local police commissioner (A.J. Brown) after the local lawmen are baffled. Meredith must apprehend the killer before he can strike again in this suspenseful crime mystery taken from the novel by Edgar Wallace. This feature first appeared in 1960.