In the first letter, dated August 26, 17 — , Walton is now the narrator for the remainder of the story. Walton tells how Victor proves his tale by producing the letters of Felix and Safie. Victor tells Walton to learn from his mistakes, that knowledge for evil ends leads to disaster. Walton comforts Victor in his last days and the two pass the time discussing other topics, such as literature, when Walton notices that it has taken a full week for Victor to narrate this story. Victor tells Robert that he must carry on the mission to destroy the monster.
In the letter dated September 2, 17 — , Walton grieves at the fact that he has found a friend who seems on the verge of death and that his own mission to discover a northwest Arctic passage has failed. He writes to his sister to remember him fondly and to wish her family well.
In the letter dated September 5, 17 — , Walton writes that Victor is now dying, and Walton has a near mutiny aboard his ship. The crew wants the ship to return to warmer waters before the ship is crushed by the weight of the ice. Walton chides the crew for their lack of adventure, and they agree to rescind their demand to turn the ship southward to escape a certain death.
In the letter dated September 7, Walton is in deep despair, now far short of his goal. He informs the crew that they will return to England if they are not destroyed.
In the last letter of the book, dated September 12, Victor wants to remain in this inhospitable climate even if Walton's ship returns home. However, Walton cannot lead the men to their deaths. Victor will not return to Europe or England without confronting his enemy. Walton knows that Victor will die soon from exhaustion and exposure. In the end, Victor dies.
The monster breaks into the ship's cabin where Victor's body lies in state. Walton and the monster startle each other and the monster begins to tell his part of the story when he began his reign of terror.
The monster finds that he can gain no sympathy from man, so he pledges to remain in the frozen north until he dies. The monster tells that he has suffered along with Victor and made evil his version of good. The monster promises no harm to Walton or his crew and leaves the ship to live out his days in the frozen land of ice. To the monster, dying is his only consolation to relieve the pain he has endured since he was given that spark of life in Ingolstadt. He swears "I shall ascend my funeral pile triumphantly and exult in the agony of the torturing flames." With this statement, the monster leaps overboard from the ship and disappears in the mist.
The letters close the "frame" in the novel. Walton's version of the story is used to make Victor's story more believable. Walton gives some validity to the story by mentioning that he sees Victor's letters and the monster.
The first letter reinforces the theme that using knowledge for evil leads to disaster. Walton and Victor also talk of literature, probably Romantic books.
In the second letter, Walton has deep feelings about failure, sounding a depressed note on his failure to accomplish his goals. He also feels a deep sense of sorrow when he does find companionship, only to lose that companion in death.
In the letter dated September 5, Walton knows the limits of his personal and physical being, but Victor still wants to press on. Victor obviously has lost his mind, as no thinking person would risk their life for something like this unless it was really self-serving.
In the final letter, dated September 12, the monster alludes to Milton's Paradise Lost by saying, "But it is even so, the fallen angel becomes a malignant devil. Yet even that enemy of God and man had friends and associates in his desolation; I am alone." The monster knows that even the Devil had a host with him for aid and comfort. Being alone drove him to commit murders for revenge to torment his creator.