There are a few changes at Hogwarts as Harry begins his third year. Hermione is taking a double courseload, including some that are taught simultaneously. Two new teachers join the staff: Professor Remus J. Lupin for Defence Against the Dark Arts and, to Harry, Ron and Hermione's delight, Rubeus Hagrid for Care of Magical Creatures. Lupin's lessons are enjoyable but Hagrid's soon become dreary. During the first class, Draco Malfoy is attacked by the hippogriff Buckbeak. Draco's father, Lucius Malfoy, files a complaint against Hagrid who then resorts to teaching them about the extremely boring animals 'Flobberworms'.
Black is still at large, and so Dementors patrol the school. Dementors drain happiness from anyone nearby, and Harry is particularly affected; he faints during a Quidditch match when they approach him and falls from his broomstick, which flies into the Whomping Willow's reach. Professor Lupin teaches him the Patronus charm to repel Dementors, should they attack him again.
Tension grows between Hermione Granger and Ron Weasley because Hermione's cat, Crookshanks, continually torments Ron's rat, Scabbers. At Christmas, Harry receives a superb Firebolt broomstick, and Hermione suspects Black is the anonymous donor. She reports it to Professor Minerva McGonagall, who confiscates the broom for testing. When the broom is returned some weeks later, the two boys try to make up with Hermione, but it goes wrong when Ron discovers Scabbers is missing; Ron blames Crookshanks. Hermione's heavy workload, meanwhile, begins to take its toll on her and she ends up doing the (for her) unthinkable: she accidentally misses a Charms class, and she drops out of another class, Divination, altogether.