The novel begins in a frame narrative: Robert Walton, the captain of a ship, recounts his adventures through a series of letters to his sister back in England. Walton encounters Victor Frankenstein in the seas near the North Pole and is told his story, and the major part of the novel consists of Frankenstein's narration of his strange adventures.
Victor tells Walton of his early life in Geneva and his close relationships with his cousin, Elizabeth Lavenza, who had come to live with his family when her mother died, and his friend Henry Clerval. Victor eventually goes to the university at Ingolstadt and begins to study natural philosophy and chemistry. During this time, he becomes consumed by the desire to discover the secret of life and finally succeeds. He fashions a creature out of old body parts and animates it one night. However, the creature appears so horrible that he runs away, allowing the creature to escape.
Shortly afterwards, Victor is preparing to return to Geneva when he receives a letter from his father telling him that his youngest brother, William, has been murdered.
Victor hurries home and, on the way, sees the monster in the woods and becomes convinced that the creature murdered William. He arrives home to find that Justine Moritz, a girl who had lived for some time in the Frankenstein household, has been accused of the murder. She is tried, condemned, and executed, despite her assertions of innocence, and Victor becomes despondent and guilty knowing that the creature he created was responsible for the deaths of these two innocent people.
Victor's father hopes to take Victor's mind off of his grief by taking the family on a trip. One day while Victor is alone in the mountains, the monster appears to him, tells his story, and begs his creator to make him another creature as a mate. Victor refuses at first, but finally gives in, convinced by the monster's persuasive pleas. After his family returns home, Victor departs on a journey for England to gather information for his creation. He secludes himself on an island and works. One night, the monster appears at his window. Struck by the horrific consequences of his work, Victor destroys the new creation. The monster is enraged and vows that he will be with Victor on his wedding night.
Later that night, Victor goes out onto the lake in a boat and dumps the remains of the second creature in the lake. The wind picks up, preventing him from returning, but in the morning he comes ashore near a town. Upon landing, he is informed that he will be tried for a murder that happened the previous night. He is led to see the body and is shocked to behold his friend Henry Clerval, with the mark of the monster's fingers on his neck. He falls ill and stays in prison until his recovery, after which he is acquitted of the crime and returns to Geneva with his father.
Shortly after his return, Victor and Elizabeth marry. Victor is...