Robert Walton, the captain of a ship bound for the North Pole, writes a letter to his sister, Margaret Saville, in which he says that his crew members recently discovered a man adrift at sea. The man, Victor Frankenstein, offered to tell Walton his story.
Frankenstein has a perfect childhood in Switzerland, with a loving family that even adopted orphans in need, including the beautiful Elizabeth, who soon becomes Victor's closest friend, confidante, and love. Victor also has a caring and wonderful best friend, Henry Clerval. Just before Victor turns seventeen and goes to study at the University at Ingoldstadt, his mother dies of scarlet fever. At Ingolstadt, Victor dives into "natural philosophy" with a passion, studying the secrets of life with such zeal that he even loses touch with his family. He soon rises to the top of his field, and suddenly, one night, discovers the secret of life. With visions of creating a new and noble race, Victor puts his knowledge to work. But when he animates his first creature, its appearance is so horrifying he abandons it. Victor hopes the monster has disappeared for ever, but some months later he receives word that his youngest brother, William, has been murdered. Though Victor sees the monster lingering at the site of the murder and is sure it did the deed, he fears no one will believe him and keeps silent. Justine Moritz, another adoptee in his family, has been falsely accused based of the crime. She is convicted and executed. Victor is consumed by guilt.
To escape its tragedy, the Frankensteins go on vacation. Victor often hikes in the mountains, hoping to alleviate his suffering with the beauty of nature. One day the monster appears, and despite Victor's curses begs him incredibly eloquently to listen to its story. The monster describes his wretched life, full of suffering and rejection solely because of his horrifying appearance. (The monster also explains how he learned to read and speak so well.) The monster blames his rage on humanity's inability to perceive his inner goodness and his resulting total isolation. It demands that Victor, its creator who brought it into this wretched life, create a female monster to give it the love that no human ever will. Victor refuses at first, but then agrees.
Back in Geneva, Victor's father expresses his wish that Victor marry Elizabeth. Victor says he first must travel to England. On the way to England, Victor meets up with Clerval. Soon, though, Victor leaves Clerval at the house of a friend in Scotland and moves to a remote island to make his second, female, monster. But one night Victor begins to worry that the female monster might turn out more destructive than the first. At the same moment, Victor sees the first monster watching him work through a window. The horrifying sight pushes Victor to destroy the female monster. The monster vows revenge, warning Victor that it will "be with him on [his] wedding night." Victor takes the remains of the female monster and dumps them in the ocean. But when he returns to shore, he is accused of a murder that was committed that same night. When Victor discovers that the victim is Clerval, he collapses and remains delusional for two months. When he wakes his father has arrived, and he is cleared of the criminal charges against him.
Victor returns with his father to Geneva, and marries Elizabeth. But on his wedding night, the monster instead kills Elizabeth. Victor's father dies of grief soon thereafter. Now, all alone in the world, Victor dedicates himself solely to seeking revenge against the monster. He tracks the monster to the Arctic, but becomes trapped on breaking ice and is rescued by Walton's crew.
Walton writes another series of letters to his sister. He tells her about his failure to reach the North Pole and to restore Victor, who died soon after his rescue. Walton's final letter describes his discovery of the monster grieving over Victor's corpse. He accuses the monster of having no remorse, but the monster says it has suffered more than anyone. With Victor dead, the monster has its revenge and plans to end its own life.