The story begins with Captain Robert Walton sailing to the North Pole in the 18th century. Unfortunately, the boat gets stuck in impassible ice hundreds of miles from land. With nothing else to do, he writes letters to his sister back in England. He’s pretty boring, as far as we can tell. He tells his sister that he wants a male friend to keep him company.
Soon, Walton’s despair is interrupted by the sight of – a man! On the ice! Riding a dog-sled! The man boards the ship, and it seems as if Walton’s wish for a friend has come true. But this new guy Victor? Kind of nuts.
Victor recounts his life story to Walton as he rests aboard the ship. Victor started out like any normal kid in Geneva. His parents adopted a girl named Elizabeth for him to marry when he was older. (That won’t be weird.) In the normal progression of things, Victor gets older and goes off to college to study natural philosophy and chemistry. He also renews his interest in alchemy. In about two years (which, by the way, is one third of a Ph.D. in the U.S.), he figures out how to bring a body made of human corpse pieces to life. Afterwards, he is horrified by his own creation (no…really?) and falls ill. Lucky for him, his friend, Henry, nurses him back to health.
Back in Geneva, Victor’s younger brother, William, is murdered. The Frankenstein family servant, Justine, is accused of killing him. Victor magically intuits that it is the monster that killed William and that Justine is innocent. Thinking no one would believe the "my monster did it" excuse, Victor is afraid to even propose his theory. Even when poor Justine is executed.
Victor, in grief, goes on a trip to the Swiss Alps for some much-needed rest and relaxation. All too conveniently, he runs into the monster, who confesses to the crime. The monster tells a sad and moving story about how he has been alienated from the world (being a corpse-parts conglomeration can do that to you), and how he killed the boy out of revenge. In short, he’s pissed off that his maker created him to be alone and miserable. He tells a story about a family of cottagers who gave him hope that he would find compassion, but how even they drove him away. He lost his last chance to connect with society. The monster asks Victor to create for him a female companion as monstrous as he. After much persuading, Victor agrees. At this point, the story is being told by the monster, as told by Victor, as told by Walton.
Victor leaves to make a new monster. He drops off Henry in Scotland while he goes to an island in the Orkneys to work. When he is almost finished, he destroys the second monster, believing he has been tricked by the first monster and that the two will bring destruction to humanity rather than love each other harmlessly. The monster sees him do this and swears revenge…again. Adding insult to injury, Victor throws the pieces of she-monster into the sea. When Victor lands on a shore among Irish people, they accuse him of murdering Henry, who has been found dead. Victor falls ill again. His father comes to visit. When he recovers, he is acquitted with the help of a sympathetic magistrate.
Victor returns to Geneva and prepares to marry Elizabeth before remembering the monster's promise to be with him on his wedding night. Victor thinks the monster is threatening him, but the night he and Elizabeth are married, the monster kills the bride instead. This death causes Victor's father to pass away from grief (as he just lost a daughter-in-law and a daughter).
Victor is as alone as the monster, and now, as bent on revenge. We can’t really tell the two of them apart anymore except that the monster is taller. And he has some funny-looking joints. Victor chases the monster over all imaginable terrain until he is ragged and near death. That’s about the time he gets to Walton’s ship. After telling his story, Victor dies. The monster comes aboard the ship, and Walton discovers him crying over the dead body of Victor. He has nothing more to live for, he says, so he goes off to die.