Harry Potter and the Second Prophecy

Professor Trelawney made two prophecies in her lifetime. The first was about Harry Potter's birth. The second was about Peter Pettigrew's escape. But what if the second one had been about someone else? The story begins in the Shrieking Shack (Chapter 19 of Prisoner of Azkaban) - Snape has revealed himself, and Harry and Ron are about to disarm him. But Hermione has other ideas...