How does Shelley return to her frame story in chapter 24?
The remainder of the book is again written in letters to his sister Margaret in Enlgland. This is where he tells of Victor's decline in health, the mutiny of his own sailors, and the visit of the creature after Victor finally passes. He records in letters the creature's conversation and also his vow to kill himself. He says that Robert is the last of his kind to see the monster with his own eyes, that the creature will build a funeral pyre and lavish in the torture of the flames. So, he does not kill himself in the novel...it happens after the book has ended, but the creature has always been a "man" of his word.
The novel begins and ends with Robert Walton writing letters to his sister.