Slaughterhouse-Five is set within a frame story: the first chapter is told from the perspective of the narrator, a stand-in for Vonnegut, who is writing a book on Dresden and World War II. The second chapter begins that book, and the rest of Slaughterhouse-Five is devoted to telling that story, with the first sentence and the last sentence exactly what the narrator from Chapter 1 promised they would be. This frame story positions Vonnegut as the narrator and blurs the line between fiction and autobiographical fiction, between reality and the world of the story.
Considering that the narrator positions himself as an unreliable narrator from the beginning of Chapter 1, the frame story leads the reader to question the implausible facets of Pilgrim's life in a way they otherwise might not without the framing device. At the same time, the autobiographical elements of the story appear to lend credence to the novel, and the science fiction elements of the story are implausible regardless of the narrator's unreliable nature. Questions of truth and fiction dominate the story as a result.
Kilgore Trout as a character further complicates the relationship between the narrator, his story, and Slaughterhouse-Five. Trout appears to be a pseudo-Vonnegut, a science fiction writer who writes cheap but not widely read stories for popular consumption. A few of these stories have similar themes and subject matter to the science fiction elements of Slaughterhouse-Five. Combined with the self-referential facets of the book, Slaughterhouse-Five suggests that storytelling is a complex endeavor that blurs the line between what is real and what isn't, and the use of a frame story both evidences and enacts this theme of the novel.