The letters Robert Walton writes to his sister Margaret Saville, which follow his journey through the Arctic, frame the novel. This is an example of a frame story, a unifying tale in which other stories appear. Walton’s letters are an important narrative device that allow readers to gain a more complex perspective on the story’s events. They serve the very practical purpose of introducing Victor Frankenstein and giving Frankenstein an opportunity to tell his story—the heart of the novel.
Letters themselves are a central motif in Frankenstein. A motif refers to a recurring element or idea in a work of literature. Besides Robert Walton’s letters to his sister Margaret, which give structure to the novel, the reader is introduced to additional letters from Victor Frankenstein and the Monster. Because Shelley offers multiple perspectives through these letters, readers have the opportunity to be drawn into characters' direct narration of events and weigh the events of the story from all sides. Letters are also used as a form of evidence. In Chapter 13, the Monster offers copies of Safie’s letters to provide proof of his story. Thus the way people tell their own stories in writing is regarded as bearing consequential weight.