Frankenstein is written in the form of a frame story that starts with Captain Robert Walton writing letters to his sister. It takes place at an unspecified time in the 18th century, as the letters' dates are given as "17—". In the story following the letters by Walton, the readers find that Victor Frankenstein creates a monster that brings tragedy to his life.
Captain Walton's introductory frame narrative
The novel Frankenstein is written in epistolary form, documenting a fictional correspondence between Captain Robert Walton and his sister, Margaret Walton Saville. Walton is a failed writer and captain who sets out to explore the North Pole and expand his scientific knowledge in hopes of achieving fame. During the voyage, the crew spots a dog sled driven by a gigantic figure. A few hours later, the crew rescues a nearly frozen and emaciated man named Victor Frankenstein. Frankenstein has been in pursuit of the gigantic man observed by Walton's crew. Frankenstein starts to recover from his exertion; he sees in Walton the same obsession that has destroyed him and recounts a story of his life's miseries to Walton as a warning. The recounted story serves as the frame for Frankenstein's narrative.
Victor Frankenstein's narrative
Victor begins by telling of his childhood. Born in Naples, Italy, into a wealthy Genevan family, Victor and his brothers, Ernest and William, all three being sons of Alphonse Frankenstein by the former Caroline Beaufort, are encouraged to seek a greater understanding of the world through chemistry. As a young boy, Victor is obsessed with studying outdated theories that focus on simulating natural wonders. When Victor is five years old, his parents adopt Elizabeth Lavenza, the orphaned daughter of an expropriated Italian nobleman, with whom Victor later falls in love. During this period, Victor's parents, Alphonse and Caroline, take in yet another orphan, Justine Moritz, who becomes William's nanny.
Weeks before he leaves for the University of Ingolstadt in Germany, his mother dies of scarlet fever; Victor buries himself in his experiments to deal with the grief. At the university, he excels at chemistry and other sciences, soon developing a secret technique to impart life to non-living matter. Eventually, he undertakes the creation of a humanoid, but due to the difficulty in replicating the minute parts of the human body, Victor makes the Creature tall, about 8 feet (2.4 m) in height and proportionally large. Despite Victor's selecting its features as beautiful, upon animation the creature is instead hideous, with watery white eyes and yellow skin that barely conceals the muscles and blood vessels underneath. Repulsed by his work, Victor flees when it awakens. While wandering the streets, he meets his childhood friend, Henry Clerval, and takes Henry back to his apartment, fearful of Henry's reaction if he sees the monster. However, the Creature has escaped.
Victor falls ill from the experience and is nursed back to health by Henry. After a four-month recovery, he receives a letter from his father notifying him of the murder of his brother William. Upon arriving in Geneva, Victor sees the Creature near the crime scene and climbing a mountain, leading him to believe his creation is responsible. Justine Moritz, William's nanny, is convicted of the crime after William's locket, which had contained a miniature portrait of Caroline, is found in her pocket. Victor is helpless to stop her from being hanged, as he knows no one would believe his story.
Ravaged by grief and guilt, Victor retreats into the mountains. The Creature finds him and pleads for Victor to hear his tale.
The Creature's narrative
Intelligent and articulate, the Creature relates his first days of life, living alone in the wilderness and finding that people were afraid of and hated him due to his appearance, which led him to fear and hide from them. While living in an abandoned structure connected to a cottage, he grew fond of the poor family living there, and discreetly collected firewood for them. Secretly living among the family for months, the Creature learned to speak by listening to them and he taught himself to read after discovering a lost satchel of books in the woods. When he saw his reflection in a pool, he realized his physical appearance was hideous, and it terrified him as it terrifies normal humans. Nevertheless, he approached the family in hopes of becoming their friend. Initially he was able to befriend the blind father figure of the family, but the rest of them were frightened and they all fled their home, resulting in the Creature leaving, disappointed. He travelled to Victor's family estate using details from Victor's journal, murdered William, and framed Justine.
The Creature demands that Victor create a female companion like himself. He argues that as a living being, he has a right to happiness. The Creature promises that he and his mate will vanish into the South American wilderness, never to reappear, if Victor grants his request. Should Victor refuse his request, the Creature also threatens to kill Victor's remaining friends and loved ones and not stop until he completely ruins him.
Fearing for his family, Victor reluctantly agrees. The Creature says he will watch over Victor's progress.
Victor Frankenstein's narrative resumes
Clerval accompanies him to England, but they separate at Victor's insistence at Perth, Scotland. Victor suspects that the Creature is following him. Working on the female creature on the Orkney Islands, he is plagued by premonitions of disaster, such as the female hating the Creature or becoming more evil than him, but more particularly the two creatures might lead to the breeding of a race that could plague mankind. He tears apart the unfinished female creature after he sees the Creature, who had indeed followed Victor, watching through a window. The Creature later confronts and tries to threaten Victor into working again, but Victor is convinced that the Creature is evil and that its mate would be evil as well, and the pair would threaten all humanity. Victor destroys his work and the Creature threatens him by saying "I will be with you on your wedding night." Victor interprets this as a threat upon his life, believing that the Creature will kill him after he finally becomes happy. Victor sails out to sea to dispose of his instruments, falls asleep in the boat, is unable to return to shore because of changes in the winds, and ends up being blown to the Irish coast. When Victor lands in Ireland, he is soon imprisoned for Clerval's murder, as the Creature had strangled Clerval to death and left the corpse to be found where his creator had arrived, causing the latter to suffer another mental breakdown in prison. After being released, Victor returns home with his father, who has restored to Elizabeth some of her father's fortune.
In Geneva, Victor is about to marry Elizabeth and prepares to fight the Creature to the death, arming himself with pistols and a dagger. The night following their wedding, Victor asks Elizabeth to stay in her room while he looks for "the fiend". While Victor searches the house and grounds, the Creature strangles Elizabeth to death. From the window, Victor sees the Creature, who tauntingly points at Elizabeth's corpse; Victor tries to shoot him, but the Creature escapes. After Victor gets back to Geneva, Victor's father, weakened by age and by the death of his precious Elizabeth, dies a few days later. Seeking revenge, Victor pursues the Creature to the North Pole, but collapses from exhaustion and hypothermia before he can find his quarry.
Captain Walton's conclusion
At the end of Victor's narrative, Captain Walton resumes the telling of the story, closing the frame around Victor's recounting. A few days after the Creature vanished, the ship becomes trapped in pack ice, and multiple crewmen die in the cold before the rest of Walton's crew insists on returning south once it is freed. Upon hearing and becoming angered by the crew's pleas to their captain, Victor lectures them with a powerful speech: it is hardship, not comfort and easiness, that defines a glorious undertaking such as theirs; he urges them to be men, not cowards. The ship is freed and Walton, owing it to the will of his unchanged men, albeit regretfully, decides to return South. Victor, even though in a very weak condition, states that he will go on by himself. He is adamant that the creature dies.
Victor dies shortly thereafter, telling Walton, with his last words, to seek "happiness in tranquillity and avoid ambition". Walton discovers the Creature on his ship, mourning over Victor's body. The Creature tells Walton that Victor's death has not brought him peace; rather, his crimes have left him completely alone. The Creature vows to kill himself so that no others will ever know of his existence. Walton watches as the Creature drifts away on an ice raft that is soon "lost in darkness and distance", never to be seen again.