Harry Snape and the Prisoner of Azkaban

Harry Snape is lucky to reach the age of thirteen. His hopes for a quiet term concentrating on Quidditch are dashed when a maniacal mass-murderer escapes from Azkaban, pursued by the Dementors who guard the prison. It's assumed that Hogwarts is the safest place for Harry to be. Is it a coincidence that he can feel eyes watching him? What is his father hiding? (Series - Year 3)