An unexpected character primarily determines the outcome of Harry Potter and the Prisoner of Azkaban’s narrative.
The Harry Potter series features a wide range of exceptional supporting characters who help to develop the plot and tie together multiple plotlines. And the cinematic adaptation of Harry Potter and the Prisoner of Azkaban is the ideal illustration of this. In the movie, the notorious killer Sirius Black escapes from Azkaban and terrorizes the Hogwarts kids while he’s on the run. But in the film, Sirius wouldn’t have attended Hogwarts if Molly Weasley hadn’t been there.
It is revealed that Sirius went back to Hogwarts to kill Peter Pettigrew, who had falsely accused him of killing their mutual friends James and Lily Potter. Since then, Peter has stayed with the Weasley family while disguising himself as his rat animagus form. Before Percy Weasley became a prefect and received an owl as a reward for his success, he was Percy’s pet. At that point, he gave Ron, his younger brother, his pet rat.

Scabbers were present to see the beginning of Harry and Ron’s friendship when they first met. However, Ron unintentionally abandons Scabbers at the railway station while traveling to school in the Harry Potter and the Prisoner of Azkaban movie. That causes Molly Weasley, his mother, to run after the moving train and give the rat to her son.
In both the novel and the movie, Ron spends the summer between his second and third years at Hogwarts with his family in Egypt. They won the lottery, which is why their family portrait, which features Scabbers, was published in the newspaper, and they can now afford the vacation. When Sirius got a copy of the newspaper, he immediately thought of Peter, an old buddy. He was sent to Hogwarts because of that. However, in the book, Ron is truly bonded to his pet and takes him on the train rather than almost forgetting about him. That was altered in the film, though, to feature the rat before the twist briefly.

Whatever the case, if Ron had forgotten Scabbers, he wouldn’t have been present at Hogwarts when Sirius arrived to exact his vengeance. Additionally, Harry would never discover who betrayed his parents and the real reason he became an orphan. That year, Ron forgetting to bring his pet rat to school would have been a tragedy because it would have altered the course of the entire series. In that regard, Molly is the unanticipated character, ensuring the plot develops and unites all the characters.

Due to Molly’s thoughtful action, Harry discovers the truth about his godfather and forges a bond with the figure who has always been his closest father. But the entire series may have developed differently if she hadn’t been such a dedicated mother. It shows how significantly all the characters in the Harry Potter series—even the minor ones—affect the plot.