Frankenstein is presented as a frame tale, told by Captain Walton while on an expedition to the North Pole, where he finds Frankenstein. Frankenstein is a scientist who created a monstrous human-like Creature. The Creature tried to explain his murders to Frankenstein, claiming that people rejected and feared him, begging Frankenstein to make him a mate. Frankenstein first agrees then destroys the mate. The enraged Creature kills Frankenstein's wife, fleeing to the North Pole. After Frankenstein dies, Walton sees the Creature mourning as he floats away on a raft.
Seafaring explorer Robert Walton describes his expedition through the Artic waters to his sister Margaret Saville in a series of letters. They find themselves in waters too icy to pass through. Here Walton discovers Victor Frankenstein, alone in a sledge on the ice. He is emaciated and dangerously ill. Walton rescues Victor, helps him to recover somewhat, and learns his story. He recounts the tale, in Victor's voice, to Margaret.
Victor begins with his childhood in Geneva, where he passes many happy years with his loving father Alphonse, his mother Caroline Beaufort, and Elizabeth Lavenza, an orphan about Victor's age who was adopted by his family. He also spends time with his best school friend, Henry Clerval. Victor becomes fascinated by alchemy at a young age. At seventeen he is about to leave for Ingoldstadt to study science, when both his mother and Elizabeth catch scarlet fever. Elizabeth recovers, but Caroline dies from the illness.
In Ingoldstadt, he studies chemistry and natural philosophy. Over two years Victor devotes himself solely to his studies, and advances rapidly. He earns the admiration of the school. He is obsessed with discovering the secret to creating life. He figures out a way to create a human being using dead human parts and combining his knowledge of alchemy, chemistry and electricity.
Victor spends months on his project, working zealously and losing all sense of time or season. Finally his monster comes to life, yet when Victor sees it move he is horrified. He flees to the streets of Ingoldstadt, and wanders the town confusedly. He runs into Henry Clerval who has come to Ingoldstadt to study, and the two return to Victor's apartment. The monster has disappeared, yet still Victor is overcome by a feverish illness.
Clerval spends months nursing Victor back to health. When he has recovered, Victor plans on returning to his family in Geneva. He receives a letter from his father asking Victor to come home immediately, as Victor's youngest brother, William, has been murdered. Justine Moritz, the family's loyal servant, has been accused of the crime. Victor hurries to Geneva, and on his way he wishes to view the place of the murder. In the woods, he sees his own monster running and he becomes convinced that the monster killed William.
The following day in Geneva, Justine is tried and found guilty of the murder. She goes resignedly to her death and Victor is overwhelmed by agonizing guilt. Looking for solace, he takes a journey in the mountains. There the monster appears again, and comes face-to-face with Victor. The monster has learned how to speak eloquently, and begs Victor for understanding. He has been shunned and despised by human society and thus has become bitter. He murdered William in an effort to punish Victor for abandoning him. He requests that Victor create a female creature as a companion for the monster, and only then will he leave Victor alone. If Victor chooses not to comply, the monster promises to bring more misery to Victor's loved ones. Victor refuses, but decides, at the monster's insistence, to listen to the monster's story.
The monster has learned how to speak and read by observing an exiled family, the DeLaceys. When he tries to interact with them, however, they are horrified and chase him away. One day, the monster finds Victor's lost notebook and letters. He learns of his creation and begins to hate Victor for having made him so hideous and causing all of his pain and grief. At the end of his tale he asks Victor to create a companion for him and Victor finally agrees.
Returning briefly to Geneva, Victor agrees to marry Elizabeth when he returns from his travels. He then heads to England and Scotland with Clerval in order to figure out how to create a female companion. Clerval goes to Scotland, and Victor travels alone to a desolate island in order to work on his hateful project. One night Victor sees the monster outside his window, watching him with a vicious grin. Victor decides to destroy his new creation, infuriating the monster. The monster promises revenge, and then cryptically vows to be with Victor on his wedding night.
Victor takes a boat out onto a lake to dispose of the parts of his female creature. A storm throws Victor's boat off course and he ends up in an unknown Irish town. He is arrested and told he will be tried for a recent murder. Victor is shown the body and is shocked to find that it is his friend Henry Clerval, with the monster's strangulation marks on his neck. Victor falls into a feverish illness and remains in prison until he recovers. A local magistrate testifies on Victor's behalf and Victor is acquitted.
Victor returns to Geneva and marries Elizabeth. On their wedding night, Victor assumes the monster will kill him, so he has Elizabeth wait for him in her room. The monster sneaks into the room and strangles her. When Victor hears her scream he realizes that the monster's revenge was to murder his bride, not Victor. He goes back to his father's house, and soon his father dies. Victor decides to spend the rest of his days tracking down the monster in order to destroy him.
Victor chases the monster northward finally reaching the Arctic Circle. This is where Victor encounters Walton's ship, and Walton rescues him.
Victor's narration of the story ends and Walton tells the rest of it to his sister in another set of letters. Victor's becomes increasingly ill and finally dies. Walton hears a voice in the room where Victor's body lies and he walks in to find the monster weeping. The monster describes to Walton how hateful, sad and lonely he has been. Now that his creator has died, the monster wishes to build his own funeral pyre. He leaps out the window onto a large piece of drifting ice, never to be seen or heard from again.