In his school class, Victor Frankenstein (Ralph Bates) demonstrates an outstanding aptitude for maths and an interest in anatomy, much to his teacher's anger. He uses his superior intelligence and some psychology to play upon the teacher's neurosis to have the class dismissed early.At their castle home, Victor asks his father (George Belbin) for more money for scientific equipment but his father refuses. Victor sabotages his father's gun causing his father to have a fatal accident the next time he goes hunting. After the funeral, Victor leaves to go to university in Vienna where he impregnates the Dean's daughter. He decides to leave early before the end of term but before he does, Victor shows his friend Wilhelm (Graham James) a severed arm attached to a scientific machine. As Victor operates the machine, the arm comes to life and moves.The stage coach of Elizabeth Heiss (Veronica Carlson) and her father Professor Heiss (Bernard Archard) is held up by robbers. Victor and Wilhelm intervene and two robbers are killed in the process. Elizabeth recognises Victor as an old school friend. After Elizabeth and the Professor leave, Victor approaches the bodies with a large knife.Back at Victor's castle, where Alys the housekeeper (Kate O'Mara) demonstrates a strong affection for Victor, Victor and Wilhelm start to unpack scientific equipment.Next day, Victor and Wilhelm are visited by policeman Lieutenant Henry Becker (Jon Finch), another old school friend, and his fiancée Maggie (Glenys O'Brien). Henry reveals that the body of one of the robbers at the hold-up where Victor saved Elizabeth was mutilated and the head removed.Alys employs another old school friend Stephan (Stephen Turner) to assist with the duties at the castle.Victor and Wilhelm test the scientific equipment. Victor says they will next need a recently dead animal in order to continue their studies. They leave to go to dinner at the house of Professor Heiss and Elizabeth. After dinner, Victor reveals he will not be returning to university although Wilhelm intends to. As they leave, Victor steals the Professor's pet tortoise for use in his experiments.Elizabeth is in love with Victor but Wilhelm is in love with Elizabeth. Back in the castle laboratory, Victor and Wilhelm kill the tortoise, attach it to the equipment and attempt to bring it back to life. At first they appear to be unsuccessful but then the tortoise bites Victor proving that the experiment has worked. Victor wants to move on to bringing a person back to life.Victor hires a grave robber (Dennis Price) to bring him a body. He and his wife (Joan Rice) dig one up and deliver the body parts but Wilhelm is becoming disgusted with Victor's methods and refuses to help any further. The grave robber and his wife read a newspaper story of a ferry capsizing and many bodies floating to the surface. He delivers several of those to Victor who dismembers them, watched secretly in disgust by Alys.Wilhelm tells Victor he is leaving and will report him to the authorities for what he is doing. At first Victor appears to comply with him but as Wilhelm starts to dismantle the apparatus, Victor switches on the electrical current killing him. Victor marks parts of Wilhelm's body for use in his experiments.Victor assembles body parts. He becomes so engrossed with his work that he stops eating meals, refuses to allow visitors and pays no attention to Alys. Eventually he realises he needs a brain. He invites Professor Heiss and Elizabeth to dinner with the intention of poisoning the Professor and using his brain. Alys threatens to blackmail Victor with what she knows and has seen, afraid that Victor may dispose of her in favour of Elizabeth.Professor Heiss dies from the poisoning and is buried. However, he has debts and his house is claimed by the bailiff (James Hayter). Elizabeth is homeless and goes to stay with Victor to Alys's dismay. The grave robber arrives with the Professor's brain and they take it into the laboratory where the grave robber accidentally sees the assembled body. As they put the brain in a jar, they notice it has a cut in it. Victor hopes it won't be significant. The grave robber wants payment but Victor needs to keep his creation a secret so he kills the grave robber by pushing him into a large tank that he uses to hold bodies and covering him in chemicals.That night there is an electrical storm and Victor uses a lightning conductor to generate sufficient electricity to bring the monster (Dave Prowse) to life. The monster is mute and unintelligent, knocks Victor unconscious and escapes from the house by breaking down the door.The monster meets a workman on the road through the forest and kills him with his spade but is witnessed by Stephan. The monster walks away before Victor arrives on a horse drawn carriage. Stephan claims his innocence and that the murderer was a monster. Victor accuses Stephan of the murder and says he will fetch the police. On the way he finds the monster and knocks it out with a large stick. The police arrive at the murder scene and Henry questions Stephan about the murder then the two of them head towards the castle where Stephan says the monster came from.Victor chains the monster up in a cell at the castle. Henry and Stephan arrive and are met by Elizabeth and Victor. With no apparent evidence of a monster to be seen, it appears Stephan may be accused of the murder.Victor attempts to train the monster, rewarding it with food when he eventually obeys.Stephan is convicted of the murder. The grave robber's wife arrives but Victor denies knowledge of her husband's whereabouts. Victor encourages her to go via a shortcut through the woods when she says she will have to report his disappearance to the police. He releases the monster to murder her along the way. The police find her body and order Stephan's execution to be postponed. Henry visits Victor but Victor maintains his pretence of innocence. Alys tries to blackmail Victor so he takes her to the monster's cell and throws her in to be murdered by the monster. Victor offers Elizabeth the housekeeper job as Alys's replacement.The monster escapes from his cell by breaking down the door and escapes from the house. He breaks down the door of a woodsman's house where there is a young girl (Carol Jeayes) inside but does not kill her. Victor arrives on horseback and the girl's father (Hal Jeayes) sends Victor off in pursuit. The monster returns to the castle and his footsteps waken Elizabeth. She goes to investigate thinking it is Victor but is attacked by the monster and faints in fright. Victor arrives, takes Elizabeth from the monster and lays her on her bed. Victor decides to give the monster an injection to put it to sleep to hide it. Henry arrives with the villager and his daughter and Elizabeth takes them all to Victor in his laboratory. Despite Elizabeth's claims of being attacked, Victor continues to maintain his innocence. The curiosity of the girl leads her to meddle with some of the scientific apparatus and she accidentally releases all of the chemicals into the large tank, on top of where Victor has hidden the monster.