In Harry's next [Occlumency] lesson, Snape sees Harry's memory of Voldemort and [Rookwood] - and gets angry with Harry for not closing his mind. As the lesson continues, Harry sees some of Snape's memories and then travels farther than ever before through the door in the [Department of Mysteries], but the lesson is interrupted by a scream and the two of them depart [Snape's office].

Harry and Snape rush to the [entrance hall], where they find an outraged Professor Trelawney, having been sacked by [Umbridge]. Soon, though, [Dumbledore] arrives - ordering that Trelawney continue to live at [Hogwarts], and presenting Umbridge with a replacement [Divination] teacher - Firenze.

Chapter 27 - "The Centaur and the Sneak" - In which Harry and his classmates have their first Divination lesson with Firenze, Marietta Edgecombe tells Umbridge of the D.A.'s meeting but suffers the effects of Hermione's jinx, Dobby warns Harry that the D.A. has been found out, and Harry denies the meetings to Fudge and Umbridge. Kingsley Shacklebolt modifies Marietta's memory, and Dumbledore takes the blame and leaves Hogwarts.

After many attempts, Harry finally delivers Firenze's message to Hagrid, though Hagrid refuses to heed the warning.

As time passes, the fifth years get more and more nervous about their approaching [O.W.L.s], and the D.A. is the only thing that seems to keep Harry going.