Plot

Mad doctor uses patients at his isolated psychiatric institute as subjects in his attempts to create longevity by surgically installing an artificial gland in their skulls, with disastrous results.

Professor Charles Conway is a mad scientist attempting to develop the proverbial fountain of youth by creating "the 17th gland". Ignoring all aspects of scientific ethics, his research subjects are people who have no family and are under the impression that the doctor can cure their depression. However, his research hasn't been successful and his subjects are turned into grotesque zombies. Some of Conway's patients begin to catch on to his scheme and intend to stop him.—Brian D. Switzer <bswitzer@uoguelph.ca>

The movie opens with the image of an old house. A light goes on in an upstairs window. A woman screams and we see Lobo (Tor Johnson) pawing at a young woman. Title and credits are shown over the old house.

A car pulls up to the old house. A man and woman exit the car and they ring the doorbell. Lobo opens the door. Dr. Loren Wright (Roy Gordon) and Grace Thomas (Allison Hayes) enter the house and are greeted by Dr. Charles Conway (John Carradine) who is walking down the stairs. Dr. Wright introduces his patient, Grace, to Dr. Conway. They walk up to the study. Dr. Conway's assistant, Dr. Sharon Gilchrist (Marilyn Buferd) stands at the desk and welcomes Grace. Sharon dismisses herself. Grace expresses her hope she can be helped with her problem and Conway assures her she is in the best place possible. Sharon returns to the study and takes Grace to her room. Dr. Wright lets slip that he will get in touch with Grace's father to get anything else she may need for her stay. Conway is angry and asks, "Father? What's this business about her father? Our agreement was that patients you brought to me where to have no relatives. No ties whatsoever!" Dr. Wright calmly tells Conway, "Grace Thomas committed suicide. Yes. Her bag and coat will be found floating in the bay."

Sharon gets Grace settled in her room. Conway and Wright toast each other with a glass of wine. Wright tells Conway he wants to see the results of the last experiment on a man named Jedrow. The two men go down to the basement to see Harry Jedrow (Harry Fleer). Dr. Wright gasps when Conway turns on a light over the chair. A man with a streak of white hair sits motionless in a catatonic state; his body is in a state of rigor. Conway advises they wait and hope the man recovers, given sufficient time. Conway concludes the radiation must be more carefully calculated and that the subjects must be younger. Dr. Wright seems anxious to restore Jedrow. He admits that Jedrow has a living relative. Jedrow's sister showed up looking for her brother at Wright's office. Conway is very angry and leaves Wright to deal with the problem. Lobo bathes Jedrow.

Conway visits Grace in her room. She explains that she is always frightened and just wants to cry. Sharon arrives with the sedative and a glass of warm milk. Conway returns to his office. Wright is preparing to leave. Sharon arrives in the office to report that Grace has been medicated. Wright is on his way out of the house, but must be reminded to take Grace's coat and bag. Dr. Wright drives off, and a man enters the grounds. He checks his revolver and hides it in some foliage. Lobo captures the man and takes him to the house. Conway questions the man. He claims to be lost and his name is Mark Houston (Myron Healey). Conway accuses him of being Frank Scott, a killer and thief wanted by the police. A detailed description had been provided by the police and a newspaper story confirmed it. Mark tries to leave but Conway offers him sanctuary in exchange for his assistance. Mark agrees to stay. Lobo escorts Mark to his room upstairs.

The next morning a man and woman are at the dining room table eating breakfast. Danny Green (Arthur Batanides) complains to Natalie Andries (Sally Todd) that his meal is cold. He continues his rant to an unresponsive Natalie, who just continues to read quietly. Lobo enters with Danny's toast. Danny is outraged that the toast is cold and tells Lobo, "You can't do anything right!" Danny and Natalie continue to bicker when Mark walks in for his breakfast. Natalie is instantly interested in this new man. She and Mark exchange stories. Natalie thinks that she maybe going home soon. Mark tires of Danny's childish behavior and tells him. Danny gets himself more excited as Sharon enters the room. She takes Danny upstairs to see the doctor. Mark leaves the dining room.

Danny is given an injection in Conway's lab. Danny settles down immediately. Mark enters Conway's office and asks if he can help. Sharon escorts Danny to his room. Mark and Conway discuss Mark's duties. Conway tells mark of his research on human glands. Lobo was one of his early test subjects on a seventeenth gland that can control aging. Conway offers Mark the chance to be the first man who can remain young forever, but mark expresses disinterest. When an appeal to vanity fails to work, Conway changes tack and threatens to turn Mark over to the authorities and a certain death in the electric chair. Conway discloses that the other patients in the house have been test subjects used to perfect the surgery. The discussion concludes and Conway swears Mark to secrecy.

Outside on the grounds, Grace and Natalie get some sun and talk. Natalie excuses herself; she has an appointment with Conway. Mark introduces himself to Grace. He asks her about the place, but since they both arrived the day before she can tell him nothing. She is reluctant to tell Mark much about herself. The two walk the grounds and chat. Sharon assesses the condition of Jedrow. She reports her findings to Conway. Dr. Wright calls Conway to report Jedrow's sister insists on knowing about her brother. Conway orders Wright to make out a death certificate for Harry Jedrow. He abruptly hangs up the phone. Sharon expresses surprise, "But he's alive!" Conway corrects her, "No, my dear. Jedrow is dead." Natalie enters the office for her appointment. Conway meets with the young lady. He tells her she has improved over the last three months. He does have one final treatment, and then she may leave in a day or two.

It is dinner time, and Mark and Grace join Danny at the dining room table. Mark is turning on the charm and inquires about Natalie. Conway joins his patients and suggests music. Conway plays a work by Bach on the organ. Lobo enters with a tray and Sharon spikes the soup with a sedative for Natalie. Mark excuses himself to check on Natalie, but he is intercepted at the staircase by Sharon. Sharon explains to Mark that Natalie is having dinner in her room, a privilege all are afforded. Lobo takes Natalie, now fast asleep, to the lab and operating room. He places her on a gurney. Sharon tells Lobo to send all the remaining patients to bed. Lobo announces, "Time for go to bed." Mark knocks on Natalie's door but gets no response. Conway directs Mark down to his own room.

Sharon and Conway prep for surgery. Sharon administers anesthetic. Mark enters Natalie's room and finds everything normal, except Natalie is not there. Conway begins surgery. He opens his test subject's neck and calls for the gland. He retrieves an object that looks like a dark shrimp from the tray Sharon is holding. We see a flat, breakfast sausage-sized object pulsating in the doctor's hand. Mark calls on Grace in her room. He tells Grace she is in danger and that Natalie is gone. Conway finishes surgery and tells Sharon they will know if it was a success in eight hours. Mark tells Grace about Conway's plan, but she does not believe Mark. Natalie is subjected to the final part of the procedure, the carefully calibrated exposure to electricity. Sharon and Conway check on Natalie eight hours later. They are disappointed to see the results. Natalie's face is a charred mess of scar tissue. Natalie wakes and moans.

Conway talks to Grace. He tells her she is improving. They talk about Natalie. Grace tells Conway that Mark is worried about her. Conway lies and tells Grace that Natalie is fine and he released her. In fact, he took her to the train himself early this morning. Conway advises Grace to avoid any further contact with Mark, "He's a dangerous man." Sharon witnesses the exchange and registers a bit of jealousy. She tells Conway she loves him, but Conway assures Sharon she has nothing to worry about. Sharon suggests Grace be the next test subject. Conway assures Sharon that when the time is right she will be.

Mark searches the house. He finds the basement entrance and descends the stairs. In a locked room he finds Jedrow. He turns on the light and examines the man. Mark returns to Grace's room, but she demands he leave. Lobo removes Jedrow's body, so when Mark and Grave arrive she does not believe Mark's story. They explore the basement and find Natalie's room. They both see the horror that Conway created. Grace recoils in horror. Mark and Grace return to Grace's room. Lobo carries a coffin outside. It contains Jedrow's body. Lobo places the box in a hole and starts to fill it in with dirt. The dog alerts Lobo to a stranger on the grounds, so he goes to investigate. Mark finds the coffin and opens it. Jedrow is still alive. Lobo returns and fills in the hole. Mark pays a call on Danny. Mark explains the situation and convinces Danny to join him later. All pretend to sleep. Conway checks on all his patients and then returns to his office. At the appointed time Danny joins Mark and Grace in the living room. Mark tells Danny to take Grace out of the house to safety, but before they leave, Conway joins them with Lobo and Sharon. Danny and Mark are escorted to the basement. Conway takes Grace to his office. Mark shows Danny Natalie in her room. Danny taunts Lobo and tells him a story to distract the dull-witted giant long enough to make their escape. Lobo is disabled, but not before shooting Danny. In the lab, Sharon preps Grace for surgery. Conway steps into his office and is confronted by Mark, who now has a gun. Conway now realizes that Mark is a policeman. He shuts off the lights and makes his escape. Mark calls the police and tells them to come to the house. Mark searches the grounds for Conway. Conway goes back into the house as the police arrive. Captain George Reagan (Guy Prescott) deploys his men to search for Conway.

Lobo escapes his room in the basement. Conway enters the living room and encounters Jedrow. Conway is shocked to see Jedrow and tells the man, "No. You're dead. I had you buried." Jedrow is holding a knife and runs the mad scientist through, killing his tormentor. Lobo disarms Jedrow just as Mark and Captain Reagan enter the room. A police officer escorts Sharon Gilchrist into the living room. She confesses that Grace is still in the lab. Lobo and Sharon are arrested. Officer Ed (Paul McWilliams) informs Reagan they've found something in the basement. Mark revives Grace. She is still on the gurney. Ed and Reagan find the body of Danny. They open the door to a freak show. Conway's other subjects are herded in a small room. They are screaming, moaning and fighting. Reagan is horrified and exclaims, "Good Lord, what if they do live forever?" Mark escorts Grace downstairs. Mark introduces her to Reagan. Reagan explains that the police have been dragging the bay for her body. Mark tells Reagan that Dr. Loren Wright is also involved. He had been supplying patients for Conway's experiments. Grace learns Mark is a police Lieutenant. We close with Mark and Grace sharing a kiss.