Throughout the book, we hear numerous warnings about Black's escape and his desire to harm Harry:
* The Ministry's warnings: The Ministry of Magic constantly warns the wizarding community about Black's escape and the threat he poses to Harry.
* Hagrid's fear: Hagrid, a close friend of Sirius, is terrified of Black's escape and worries for Harry's safety.
* The news reports: Newspapers and radio reports constantly focus on Black's escape and the danger he presents to Harry.
* Lupin's reaction: Remus Lupin, the Defence Against the Dark Arts teacher, shows a peculiar interest in Black's escape and his involvement in the events.
This constant focus on Sirius Black and the danger he poses to Harry creates a sense of anticipation and suspense. We are constantly reminded that something bad is going to happen to Harry, leading us to wonder exactly what will happen and how.
This foreshadowing is crucial to the story's plot, as it builds up to the climax where Sirius Black is revealed not to be the villain, but rather a victim himself. It also highlights the danger that surrounds Harry, highlighting the importance of the events that transpire and the protection he receives from those he trusts.