Boris Karloff is fun to watch as he goes between a mild mannered doctor to mad scientist to serial killer. Maybe it was an oversight but through much of the movie he wears squeaky shoes. Look for character actor Don Beddoe towards the end as homicide cop Captain McGraw.
Dr.John Garth is on trail for mercy killing. As his daughter Martha (Evelyn Keyes) and his assistant Dr.Paul Ames (Bruce Bennett) look on he gives an impassioned speech about old age and how he’s trying to create a serum that will halt it. He refers to old age as a disease. The judge doesn’t buy it and gives him the death sentence.
In the warden’s office he’s introduced to an admirer. He’s Dr.Ralph Howard (Edward Van Sloan). The warden gives permission for the two to work together during the last three weeks of Garth’s life. He’s getting close to developing the serum. The two work in a lab guarded by Anson (Kenneth MacDonald) Trustee Otto Kron walks in but he’s told to stay out and never go in there.
In order to perfect the serum he convinces Howard to get the blood of a triple murder about to be executed. Then he persuades Howard to inoculate him. Garth’s got twenty-seven minutes to go before his date with the hangman. The warden comes to get him with a few minutes left. The phone rings. It’s the governor. His sentence has been commuted to life. Too bad. The serum works and Garth starts getting younger.
His personality changes at times and it makes him hostile. He ends up killing Howard. Otto walks in. He and Garth duke it out in a speeded up fight scene. Garth gets the best of Otto along with a head injury. He wakes up in the infirmary with no memory of the incident. Otto is blamed for killing Howard and Garth is pardoned because of his experiments.
After being back home for a while he invites three old friends over. The emphasis is on old. One is classical pianist Victor Sondini. He gives a recital. Garth says he’s slowing down as are all three. He offers to inoculate them with his serum. They turn him down. That awakens the killer in Garth.
Boris is just great with his facial expressions and that soft manner of speaking that can turn menacing at any moment. See this one.