Harry awakens in the hospital ward to hear Snape boasting about his heroic act of saving the three students from both a werewolf and Sirius Black. Cornelius Fudge's voice sounds, promising Snape an award for his courage. Ron is still unconscious, but Harry and Hermione leap out of bed and begin explaining what they saw and heard, and about Pettigrew's appearance and Black's innocence. Snape waves this away, saying that Black must have confounded their minds. Harry and Hermione are still heatedly defending Black when Dumbledore enters the room and says that he must speak with the two of them alone. Once the others have left, Dumbledore tells Harry and Hermione that he has heard Black's story and that he believes it, but that not one shred of evidence exists to back it up. He says meaningfully that they need more time to save two lives that night, and Hermione nods. When Dumbledore leaves, Hermione turns an hourglass on a chain backwards three times, taking Harry and her into the Forbidden Forest, where they hear themselves and Ron visiting Hagrid. Hermione explains in a whisper how she was given this time- turning device so that she could take more than once class at the same time, and how it is of utmost importance that nobody, especially not their past selves, sees them while the are in the form of their future selves.
The second life to which Dumbledore refers, Harry determines, is Buckbeak's; so Harry and Hermione wait quietly by Hagrid's cabin, untying the hippogriff once the executioners have gone inside the cabin to deal with some paperwork. Harry, Hermione, and Buckbeak hide in the forest as they hear the thud of an axe swung in frustration at having lost the victim, as well as Hagrid's howl of joy at the surprise escape. They wait in the woods, watching themselves go down the Whomping Willow and back up, and while Hermione and Buckbeak hide in Hagrid's empty cabin from the werewolf, Harry slips out to see who conjured the patronus. He watches the Dementors approach and attempt to kiss him, and nothing happens- no patronus is conjured. At this moment, Harry realizes that it was he who had conjured it, not his father, as he had suspected, and so he conjures it again, saving his, Hermione's, and Black's life, and finally understanding that the form of his patronus is a stag, Prongs, his father's animagi form. Father and son regard each other, then the shape disappears. Harry rejoins Hermione, and together they fly on Buckbeak's back up to the tower room where Black is being held, and they send Black and Buckbeak flying away together to their freedom.
Harry and Hermione make it back into the hospital ward only minutes before Dumbledore leaves, exactly when they turned the time back. They confide their feat to Dumbledore, who naturally is very pleased. Snape however, is most displeased when word gets out that Black escaped. Snape rages into the hospital wing, madly accusing Harry of setting him free until the other teachers force Snape to leave; we soon discover that Fudge retracted the award that he had promised to Snape. That night, Fudge removes all of the Dementors from the school grounds.
The next day is calm, until Hagrid informs Harry, Ron, and Hermione that Buckbeak escaped, and then that Lupin has resigned from the school. Harry runs to visit him as he is leaving the castle, and he listens as Lupin explains in his usual good-natured manner that after the events of last night, he really shouldn't be allowed near students during his transformations. Dumbledore catches Harry leaving Lupin's office and talks with him for a bit, explaining that it is no coincidence that his patronus takes his father's animagus shape, and that Harry has done a wise thing by setting Pettigrew free. Harry is confused and a bit sad as he boards the train back to London.
On the train, Hermione announces that she will drop down to a normal course load for the next semester, and Ron begins planning for Harry to stay with him for the summer. All of a sudden, a small, fluffy owl bumps against Harry's window, and he discovers in its beak a note from Sirius Black, saying that he is safe, that he did in fact send the Firebolt, and that Ron is to keep the owl as a replacement for his lost rat. In addition, Black has enclosed a note giving Harry permission to visit Hogsmeade the following year. Harry returns to the Dursleys anticipating a better summer than the last one.
This part gets slightly confusing because Harry and Hermione are themselves and yet are watching themselves at the same time. They are not allowed to interfere with the past, a fact that Harry finds immensely frustrating as he sits still watching Snape pick up his invisibility cloak. This time-turning places a new spin on an old theme; wizards are always hiding themselves and their goings-on from Muggles, who would be alarmed by the existence of anything that they could not explain simply, through their notions of science and convention. All wizards are perpetually hidden, but Harry and Hermione are doubly-hidden, keeping themselves out of sight lest other wizards see them and be alarmed at not having an explanation. This makes a good point about humans in general, who tend to fear what they cannot quickly fit into a rational scheme of life, and this extend over Muggles, who know no magic, and here over wizards, who know only the magic within their reality. As steady and prepared as Harry and Hermione are, we are to assume that they would not have fared well seeing their future selves return to the scene of the past. Liminal situations are potent, but frightening.
The end ties up neatly, but it feels heavier than the ending of past books, simply because the work is not yet all done—Sirius Black is still considered dangerous, and Peter Pettigrew, who actually is dangerous, is loose again. But the year has ended and Harry has done and learned everything he can. He returns to the Dursleys with the ability to drop Black's name whenever he wants to get something out of his uncle or cousin, and he dutifully will await his return to Hogwarts in the fall.