Approaching his third year at Hogwarts, Harry Potter has had enough of his muggle relatives. He runs away from them (finally) and enters his third term facing trouble from more than one side: for using magic outside the school and from the news that a notorious criminal, serial killer Sirius Black, has escaped the wizard's prison at Azkaban and apparently is headed for Harry. The school calls in supernatural help against Black in the form of Dementors, but unusual things continue to put Harry in peril. He is thrown into a confusing panoply of shifting alliegences and shifting shapes where nobody is who or what they seem. Who is the real criminal? What is the real crime? Who is telling or knows the truth?