Harry arrived at Hogwarts after having a very eventful summer. He had Engorged his Muggle "aunt" Marjorie Dursley, as well as the escape of the wrongly convicted Sirius Black, whose plot after escape from Azkaban was reportedly, to kill Harry.

Former Minister for Magic Cornelius O. Fudge (MOM 1980-1995) on the Black Escape

"Well, when we had put Black in the cell, we had no idea that he'd get out. It turns out that that Potter kid used a TimeTurner to save a Ministry-executed hippogriff, and used that same hippogriff to free Black. Of course, Black is dead, now...one last thing we have to worry about. But it was a serious risk Mr. Potter and Ms. Granger took...and yet they succeded. Young, dumb luck, I say."

A new addition to the Hogwarts Faculty was Harry's father's friend, and also friend of Mr. Black, Remus Lupin. Lupin perished in the Battle of Hogwarts alongside his wife Nymphadora "Tonks". Due to Black's escape from Azkaban, the Ministry had placed Dementors around Hogwarts, and their interference caused Lupin to teach Harry the Patronus Charm, widely known as a Dementor-Repellant.

Black was found on the school grounds, and was captured by the Ministry, ready for the Dementor's Kiss, in the process injuring Mr. Severus Snape, Hogwarts Potions Master.

Black was saved, and so was the life of Mr. Rubeus Hagrid's hippogriff, Buckbeak, due to a trip back in time with TimeTurners. It turns out that the entire supply of the British Ministry of Magic's TimeTurners were destroyed in the Battle of Mysteries, another bout that Potter and Granger were involved in.