Sirius Black has escaped from Azkaban prison to kill Harry. Dementors are all over Hogwarts by order of the ministry. But at the same time, Harry and Tom and Jerry learns more about the Potter family and the Marauders. And Harry and Ginny's relationship has increased.
A secret chamber has been opened at Hogwarts and has endangered the muggle born students. Harry and Ginny and Neville and Luna and Tom and Jerry must find out who and what is behind the attacks before it's too late. Meanwhile, a house elf is doing everything he can to keep Harry away from the school.