Chapter 12 - "The Patronus" - In which both Harry and Ron are angry with Hermione for reporting the Firebolt to McGonagall, Oliver Wood tries to get it back, classes resume, Lupin teaches Harry the Patronus Charm to use against Dementors, Harry asks repeatedly about his Firebolt and finally gets it back, and makes up with Hermione just as Ron finds bloody traces of what he thinks is Scabbers.
A New Broom
On Christmas morning, Ron and Harry tear into their presents - and Harry quickly discovers he's received a [Firebolt]. Hermione arrives and expresses her concern over its origin, but before the conversation can finish, Crookshanks goes after Scabbers, outraging Ron.
[Dumbledore] greets everyone at Christmas dinner, for which all of the remaining students and faculty sit at a single table. After pulling some amusing crackers, Professor Trelawney arrives and spends the rest of the meal at odds with Professor McGonagall, until finally Harry and Ron decide to depart.
Harry and Ron return to the common room and the [Firebolt], but shortly Hermione arrives with Professor McGonagall. McGonagall inspects the broom and takes it from Harry, over a concern she shares with Hermione - that the broom was sent by Sirius Black.
Following the first Defence Against the Dark Arts class of January, Harry asks Lupin again about anti-[dementor] lessons, and Lupin sets their first time for Thursday evening. When he walks away, though, Ron wonders aloud why Lupin looks ill, and Hermione impatiently implies that she already knows.