Robert Walton, an explorer, tells how he has met Victor Frankenstein in the Arctic after earlier having seen a 'gigantic figure' crossing the ice.
Victor tells of his childhood and his caring family, particularly of his love for his foster sister Elizabeth. His mother dies of fever just before he leaves to study at university.
While at university, Victor's interest in science becomes an obsession. Victor uses dead bodies to experiment on and creates a monster made of body parts. He is immediately disgusted by the thing he has created and abandons it.
Victor's brother William is murdered and Justine Moritz, a family servant, is executed for it. However, Victor believes the Monster is to blame after witnessing it at the scene of the murder.
The Monster and Victor meet in the Swiss mountains. The Monster tells the story of how it has survived and of the time it has spent becoming educated.
The Monster asks Victor to admit responsibility for his actions and show some sympathy. He also pleads with Victor to build a female companion. Victor agrees.
Victor finds a remote spot in the Orkneys where he begins to construct the female creature but suddenly, realising the consequences of what he is doing, he tears it to pieces. The Monster, who has followed Victor, is enraged and in revenge kills Victor's best friend, Henry Clerval.
Victor and Elizabeth marry, but Victor finds his new wife dead at the hands of the Monster. He vows to hunt the creature down.
In Walton's last letters, back in the Arctic, Frankenstein dies and the Monster, still miserable, heads off, probably to its own death.
Written at a time of great social change, Frankenstein is about the power of scientific ambition and the dangers of going a step too far.