Robert Walton, the captain of a ship en route to the North Pole, writes a series of letters to his sister in England, updating her on the status of his perilous mission and detailing its various challenges. After an initial period of success, the project was soon derailed as seas filled with insurmountable ice appeared. Walton, who is cornered, comes across Victor Frankenstein, who has been making his way over the ice in a sled pulled by dogs and is suffering from the effects of the cold. Walton brings him aboard the ship, assists in nursing him back to health, and then listens to the fascinating story of the monster that Frankenstein built.
In the beginning, Victor talks about his childhood in Geneva. At the conclusion of a carefree childhood spent in the company of Elizabeth Lavenza (his cousin in the 1818 version, his adoptive sister in the 1831 edition), as well as his close friend Henry Clerval, Victor enrols at the university of Ingolstadt to study natural philosophy and chemistry. After a number of years spent researching, he eventually comes to the conclusion that he has discovered the key to eternal life and is persuaded that he is the first person to have discovered it.
Victor, now armed with the knowledge he had spent so much time pursuing, spends months furiously fashioning a creature out of old body parts in order to prove his theory. The climatic moment occurs when he brings his creation to life one night, while alone in the privacy of his apartment. The sight of the abomination that he has made, on the other hand, terrifies him every time he looks at it. After a restless night of sleep that was disrupted by the spectre of the monster hovering over him, he eventually ran out into the streets and wandered in regret. Henry has travelled to the university to further his education, and when Victor bumps into him, he invites his friend to accompany him back to his flat. Despite the fact that the monster is no longer a threat, Victor becomes ill with a fever.
Victor, repulsed by the awful act he has committed, makes preparations to go back to Geneva to be with his family and go back to good health. However, just before he leaves Ingolstadt, he gets a letter from his father in which he is informed that his youngest brother, William, has been killed. Victor, overcome with sorrow, rushes hastily home. He gets his first glimpse of the monster as he is travelling through the same woods where William was killed, and after seeing it, he becomes certain that the monster was the one who killed his brother. When Victor arrives in Geneva, he learns that Justine Moritz, a sweet and mild-mannered girl who had been adopted by the Frankenstein household, had been accused of something. In spite of her protestations of innocence, she is brought to trial, found guilty, and sentenced to death. Victor’s sense of hopelessness and guilt deepen as he realises that the monster he has created is responsible for the deaths of two people he cares about who were innocent.
In the hopes that it may help him cope with his loss, Victor goes on a trip to the mountains. The monstrosity confronts him when he is travelling across a big glacier one day when he is alone himself. The monster freely admits to having killed William but implores the audience for compassion. He claims that he attacked William because he was lonely, rejected, and desolate and that he was making a desperate attempt to damage Victor, his cruel creator. The monstrous creature begs Victor to fashion him a mate, another monstrous creature of similar grotesquery who will be his constant companion.
At first, Victor is opposed to the idea since he is repulsed at the thought of creating a second monster. However, because of the monster’s eloquence and persuasiveness, Victor is eventually won over by his argument. Following his return to Geneva, Victor, accompanied by Henry, travels to England with the intention of gathering knowledge that can be used in the fabrication of a female monster. After abandoning Henry in Scotland, he relocates to an uninhabited island in the Orkneys, where he lives in seclusion while he begrudgingly attempts to replicate his earlier success. When Victor is troubled about the ethics of his behaviour one night, he peers out the window and sees the monster peering in at him with a terrifying grin on its face. This causes Victor to question the morality of his activities. As soon as Victor realised the potential repercussions of his work, he tore down the new thing he had made. The monster, fuming with wrath, swears that he will exact his vengeance by being present with Victor on the night of the latter’s wedding.
In the later hours of that day, Victor uses a boat to get to a nearby lake, where he then throws the carcass of the second beast into the water. A strong wind stops him from making it back to the island where he was staying. In the morning, he discovers that he has washed up on the shore close to a town that he is unfamiliar with. Upon landing, he is taken into custody and told that he would be tried for a murder that was discovered the night before. Victor denies having any knowledge of the crime, but when he is shown the body, he is astonished to see that his friend Henry Clerval was the one who was killed and that the mark of the monster’s fingers was on his neck. As soon as Victor recovers from his illness, which causes him to become delirious and feverish, he is declared innocent of the crime for which he was arrested.
Victor weds Elizabeth not long after he and his father got back to Geneva and settled down there. He is terrified of the warning given by the monster and believes that he will be slain on the night of his wedding. Because he wants to play it safe, he tells Elizabeth to go somewhere and wait for him. During the time that he is waiting for the monster, he hears Elizabeth scream, and at that moment, he knows that the monster was not threatening to kill him but rather his new bride. After Victor has returned home, his father suffers a heart attack and passes away a short while later. Victor makes a solemn oath that he will spend the rest of his life tracking down the monster and exacting his vengeance, and he immediately sets off on his journey to begin his mission.
As the monster travels further north into the ice, Victor follows it. During their pursuit on dogsleds, Victor is getting close to catching up to the monster, but just as they are about to do so, the sea level rises beneath them, breaking the ice and creating an insurmountable distance between them. Walton finally comes face to face with Victor at this juncture, and the story catches up to the period of Walton’s fourth letter to his sister at this point.
The remaining parts of the story are detailed in a second set of letters that Walton writes to his sister. When the two men meet, Victor is already ailing, but his condition quickly deteriorates and he passes away not long after. Walton is shocked to discover the creature weeping over Victor when he returns to the room where the body lies many days later. The room is the same room where the body was found. Walton learns from the monster about the terrible loneliness, suffering, hatred, and guilt that he has endured throughout his life. He claims that now that his creator has passed away, he too is free to put an end to his torment. After that, the monster travels to the furthest northern ice to perish there.