This enjoyably twisted British thriller was shot back-to-back with the equally warped Haunted Strangler and is one of the first films of any genre to address the subject of drug addiction. It stars Boris Karloff as Dr. Thomas Bolton, a London surgeon who believes he has developed a safe and effective anesthetic serum which he hopes will revolutionize the world of medicine. Unfortunately, a demonstration of the drug before a panel of his peers ends in a horrific mishap -- with his patient awakening under the knife -- and he is forced to leave his position in disgrace. To complicate matters, Bolton has become addicted to his own concoctions and is forced to enter an illicit arrangement, forging death certificates for a pair of grave-robbers (including Christopher Lee) in exchange for a regular fix and the means to continue his experiments. As one would imagine, this shady partnership leads him further down the road to ruin, culminating in his unwitting participation in murder -- for which he becomes the victim of a blackmail scheme. Karloff's multi-layered performance is one of his finest, bringing a great deal of pathos to his tragic character. This film was also something of a turning point for Lee, who had already risen to international fame in many Hammer productions by the time this film was acquired by MGM for American distribution.