Larry Talbot finds himself in an asylum, recovering from an operation performed by the kindly Dr. Mannering. Inspector Owen finds him there, too, wanting to question him about a recent spate of murders. Talbot escapes and finds Maleva, the old gypsy woman who knows his secret: when the moon is full, he changes to a werewolf. She travels with him to locate the one man who can help him to die - Dr. Frankenstein. The brilliant doctor proves to be dead himself, but they do find Frankenstein's daughter. Talbot begs her for her father's papers containing the secrets of life and death. She doesn't have them, so he goes to the ruins of the Frankenstein castle to find them himself. There he finds the Monster, whom he chips out of a block of ice. Dr. Mannering catches up with him only to become tempted to monomania while using Frankenstein's old equipment.
In Llanwelly village, two grave robbers break in the crypt of Lawrence "Larry" Stewart Talbot to steal his possessions. When they open the casket, they find the body covered with wolfbane and they are attacked by a creature. Soon Talbot awakes in Cardiff at the Queen's Hospital recovering from a surgery performed by Dr. Mannering and Inspector Owen is ready to interrogate him about recent murders. Talbot flees from the hospital and seeks out the gypsy Maleva, who knows that he is a werewolf, asking her to help him. Talbot wants to die and they travel to find Dr. Frankenstein. Talbot transforms into the werewolf and falls into the frozen catacombs of Dr. Frankenstein's castle. He finds the Monster frozen and he breaks the ice and release it. Soon Talbot discovers that Dr. Frankenstein is dead and he seeks out the daughter of Dr. Frankenstein, Baroness Elsa Frankenstein, expecting to borrow his journal that contains the secret of life and death. Meanwhile Dr. Mannering arrives in the village following the blood track left by the werewolf. When Elsa lends the diary of her father, Dr. Mannering prepares the equipment to drain power from Talbot to the Monster. But he becomes insane with the power on his hands and the experiment goes wrong.
Graverobbers open the grave of the Wolfman and awake him. He doesn't like the idea of being immortal and killing people when the moon is full, so he tries to find Dr. Frankenstein, in the hopes that the Dr. can cure him, but Frankenstein is dead and only his Monster is alive and this one wants to live, not to die like the Wolfman.
After being awakened, Larry Talbot chips Frankenstein's Monster out of a block of ice. When Talbot changes to the Wolf Man, the two creatures battle each other.
- The movie opens with the view of a full moon in a graveyard. As a rave squawks two grave robbers break into Larry Talbot's (aka The Wolfman- Lon Chaney Jr.) mausoleum. even though Larry has been dead for four years, his body is fully preserved. As the moon light hits the body, Larry comes to life and transforms. He kills the closer grave robber and the second one escapes. Later, the Wolfman is seen in a near by town and is confronted by a police officer. The beast runs down an ally and the officer meets his demise. Later , Larry finds himself in a hospital with a big wound on his forehead. Dr. Mannering talks with him and Larry talks about his curse. Inspector Owen (from the police department) thinks Larry is crazy and the Dr. thinks that Larry believes that he is a murdering wolf, because of his head injury. As Larry insists on the truth, the Dr. and the inspector go to Larry's hometown to prove that the real Larry Talbot is dead. However, they see that the body is gone and a picture of Larry looks exactly like the man in the hospital. Dr. manning then calls the hospital to check on Larry, only to find that he bit through his straight jacket and escaped through the window. The wolf kills again and then finds Maleva, the old gypsy woman from The Woflman (1941). They start on an adventure the Velaria to seek the help of Dr. Frankenstein. Larry wants only to break the curse and die.On the way, Larry turns again and runs from the carriage so Maleva hurt not be attacked. After turning, he kills yet again and then passes out in the frozen ruins of Frankenstein's Castle. There he finds the infamous Monster and revives him. Larry, in his human form befriends the monster. Together they search the castle from Frankenstein's records and writings about the undead. They don't find what they need. Later, Larry meets with the Baroness, Dr. Frankenstein's descendant about buying his castle. the Baroness declines but Larry agrees to meet her again at the festival of the new wine, the town's biggest event. At the event Dr. Mannering appears and confronts Larry. Larry is using an alias and refuses to go with the Dr. to get help. then Larry explodes in angry and causes a scene. Just then, the town's attention turns to the arrival of the other undead visitor, The Monster. The villagers try to attack the monster and Larry helps him escape. They return to the castle and are soon joined by the baroness and the Dr. The Dr. promises to help both "men" as the Baroness finds her father's book. The villagers take Maleva as a prisoner and questioner her about what is going on.They figure it out and Vasec decides to go against the level headed Mayor and take matters into his own hands. Vasec leaves his bar and disappears. meanwhile Dr. Mannering has both the Monster and Larry strapped to two separate slabs. he promised to drain both of their energy and destroy both Monsters. Then the Dr. changes his mind and becomes obsessed with Dr. frankenstein's dreams and reverses the energy and powers up the Monster. Larry looks up at the full moon as the Monster breaks out of his straps.The Monster immeadiately sees the Barones and grabs her. Larry transforms again and breaks out of his straps. he attacks the Monster who drops the Baroness. Finally Vasec Blows up the dam above the castle as the two titans battle. The monster throws a heavy piece of equipment at the Wolfman and the two spar back and forth. Then, just before the water bursts through the castle walls, the Wolfman climbs to a ledge to jump on the Monster and gain the upper hand. The Dr. grabs the Baroness and both flee before the flood wipes out the castle and take the two legends of horror with it.