The characters found in The Twisted Window differ from the normal characters of a suspense novel. Each one occupies two varying points of view before the book's conclusion. When good-looking Brad arrives in Winfield, Tracy, as a normal teen-age girl, is flattered by his attention, but knows he is not what he seems. Although he introduces himself as a new high school student, a little investigation proves he is not enrolled at Winfield High. Tracy discovers that Brad is there not to socialize, but for the very serious business of reclaiming his half sister. She is sympathetic to Brad, but due to her mother's recent death, and what she feels is her father's rejection, Tracy distrusts everyone's motives. Even so, she soon comes to identify with Brad, as she discovers he is also from a divided home. Her early rebellious attitude toward adults leads her to join Brad in his outlandish scheme to kidnap a local youngster, but Tracy's intelligence later allows her to understand there is a problem with Brad's story. Finally, her empathy for Brad helps her aid him in a crucial, life-saving realization.

At his first appearance in the novel, Brad is a self-confident brave young man. He relates to Tracy the "kidnapping" of his half sister by his bum of a stepfather. His vivid imagination leads him to describe a picture of his mother's suffering at his stepfather's hands. This causes Tracy to immediately identify her mother with Brad's mother, because she blames her own father for many of her dead mother's problems. Seemingly sincere about reclaiming his "stolen" half sister for his mother, Brad is convincing enough to make Tracy an ally who helps him take his half sister from her present home. But immediately, Brad develops a curious "blindness" toward what Tracy sees as the facts. When she understands she has helped kidnap a child who is in reality not Brad's half sister, her discovery forces Brad to confront some disagreeable facts. Rather than a villainous kidnapper, Brad is instead a long-suffering victim of his own guilt. His true identity is revealed in a suspenseful plot twist which includes a new character who will also surprise Duncan's readers.

The supposed "bad guys" at the beginning of the novel: Brad's stepfather, Gavin; Gavin's sister and her husband, the Carvers; and Tracy's own aunt and uncle, Rene and Cory, assume different personalities as the reader's perspective alters. Brad's family's negative history is revealed to be only a product of his fantasy, and Tracy's father's sincere concern emerges by the end of the book. Brad's own mother is revealed only through the conceptions of others and one long-distance phone conversation with Tracy. Her personality, also, differs from that which Brad describes.

The book's theme is not difficult to detect. Appearances are all important, as evidenced by the scene Tracy views through the flawed window. Forgiveness of oneself is displayed when Brad finally confronts truth in the final pages of the novel. The loyalty of true friendship is represented by Jamie, and ideas about home and family become most positive when Tracy finally associates "a vision of Winfield" with the word "home."