The following morning, company cars from the Ministry of Magic drive Harry, Ron, Hermione, and the Weasley family to King's Cross Station; this special treatment is unusual. They all walk through the divider between platforms nine and ten, onto platform nine-and-three-quarters, where they catch the Hogwarts Express train to school. As the train is leaving, Mr. Weasley pulls Harry aside and warns him not to go looking for Black. On the train, Harry tells Ron and Hermione what he has learned about Black, while a shabby- looking man snoozes in their compartment near a briefcase that reads R.J. Lupin. The friends then change the subject to Hogsmeade, and Harry again feels distraught at not being allowed to go.
During the rest of the ride, Crookshanks attacks Scabbers, and Draco Malfoy, Harry's nemesis, begins to taunt Ron for his family poverty. He halts when he sees a teacher, Lupin, sleeping within hearing range. All of a sudden, the train stops and all the lights go out. A tall, robed creature enters Harry's compartment, and Harry feels a painful, intense, miserable cold feeling and hears screams. He passes out. He wakes to explanations that the creature is a Dementor, one of the guards of Azkaban, and that Lupin sent it away by sending something silvery in its direction. Lupin gives chocolate to him and to the other shaken students, and soon afterwards they all arrive at Hogwarts.
At Hogwarts, Harry and Hermione are pulled aside by Professor McGonagall, first to check up on Harry's state after his response to the Dementor, and then second to discuss something privately with Hermione. Harry and Hermione return to the Great Hall for dinner and to hear Dumbledore, the headmaster, announce grudgingly that the castle entrances will be guarded by Dementors as precautions against Black. Dumbledore proceeds to say that several new appointments have been made, Lupin as the new defense against the dark arts teacher, and Hagrid as the new care of magical creatures teacher. The feast then begins, and Harry feels warm and content being back at Hogwarts.
At breakfast the next morning, Malfoy and his cronies are still taunting Harry about the Dementor, and Harry ignores them while he, Ron, and Hermione prepare for class. Hermione is signed up for three classes that meet at nine o'clock, but when Ron questions her, she changes the subject. The three friends troop up toward the tower where Divination meets, and after many stairs and turns, they are led to the classroom by a short and belligerent knight named Sir Cadogan.
In Divination, Professor Trelawney makes a few misty predictions about the future before instructing the class to drink tea and interpret the leftover tealeaves. Ron and Harry amuse themselves with faulty readings until Professor Trelawney joins them and finds a Grim, the black dog who haunts churchyards and is seen as a death-omen, in Harry's cup. This finding alarms everyone except for Hermione, who is skeptical and somewhat flippant about the whole situation. The class silently leaves Divination and attends Transformation with Professor McGonagall, who reassures Harry by telling the class that each year Professor Trelawney has predicted one student's death, and so far none have come true. The next class is Care of Magical Creatures, and Hagrid introduces them to a collection of animals called Hippogriffs that are half-horse and half-eagle. Harry volunteers to approach one called Buckbeak, and follows Hagrid's instructions to bow respectfully to the beast before riding on its back. When Harry returns to the ground, Malfoy taunts Buckbeak, who attacks him. Hagrid carries the bleeding Malfoy to the hospital wing. Harry is quite distraught, mostly because Malfoy has been boasting to his friends how he could persuade his father to get Hagrid fired from his job. That night, Harry, Ron, and Hermione visit a drunk, teary-eyed Hagrid, who suddenly roars fearfully that Harry should not be wandering around the grounds at night, before escorting them all back to the castle.
These two chapters contain a great deal of foreshadowing. The Dementors pose a threat for Harry, who has a store of unconscious memories that are loosened when the Dementors come near. J.K. Rowling said in an interview that she made Dementors representative of depression, with its all consuming darkness and cold, its isolation and regeneration of old fears. Harry must learn to grapple with these creatures during his year at school. The Grim in Harry's teacup plays a recurring role in the plot. Not only does Harry see it many times when he is near death, but he also sees it roaming the grounds at night. The fact that Hermione is taking three classes at nine o'clock, suggests that some magic must be involved, though we do not yet know what it is. The crisis of Buckbeak also originates in Chapter Six, when, provoked by Malfoy, the hippogriff attacks, changing the course of Hagrid's career and of its own free life.