This chapter is depicted pretty well in the films, with just details from the books missing that expand the story and characters. There’s not a lot missing that’s a big loss, but it’s a case of what they’re able to fit in the time allotted.
Dumbledore had convinced Harry not to go looking for the Mirror of Erised again, and for the rest of the Christmas holidays the invisibility cloak stayed folded at the bottom of his trunk. Harry wished he could forget what he’d seen in the mirror as easily, but he couldn’t. He started having nightmares. Over and over again he dreamed about his parents disappearing in a flash of green light, while a high voice cackled with laughter.
Harry tells Ron about the dreams, and Ron sees that as all the more of a reason not to look in the mirror again.
Hermoine returns from break, and they continue skimming books looking for any mention of Nicolas Flamel. Harry has even less time, since he’s practicing Quidditch. The next match coming up has Professor Snape acting as referee, something the entire Gryffindor team dreads.
The rest of the team hung back to talk to one another as usual at the end of practice, but Harry headed straight back to the Gryffindor common room, where he found Ron and Hermione playing chess. Chess was the only thing Hermione ever lost at, something Harry and Ron thought was very good for her.
Again, we get a lot more of the kids just being kids in the book, which is nice.
Speaking quietly so that no one else would hear, Harry told the other two about Snape’s sudden, sinister desire to be a Quidditch referee.
“Don’t play,” said Hermione at once.
“Say you’re ill,” said Ron.
“Pretend to break your leg,” Hermione suggested.
“Really break your leg,” said Ron.
The idea of Snape being a Quidditch referee was omitted from the films, as is the way the students regard him. We all knew the kids hated him as a teacher, but here they are quite afraid for Harry, in that breaking his leg would be better than playing in the match. Of course, now, knowing the ending of the series, we know that Snape’s desire to be there was to secretly protect Harry.
This is followed by Neville Longbottom returning to the Gryffindor common room having been “leg-locked” by Draco Malfoy. Hermoine performs a counter-curse on him, but he’s too afraid of something worse to go to Professor McGonagall about it.
“There’s no need to tell me I’m not brave enough to be in Gryffindor, Malfoy’s already done that,” Neville choked out.
Again, with knowing how things end, particularly how Neville stands up to Voldemort once they think Harry is dead, we know that Neville is in the right place in Gryffindor.
To console his friend, Harry goes to give Neville the last chocolate frog he got from Hermoine for Christmas. It’s then that it dawns on him where he heard the name Nicolas Flamel.
“I’ve found him!” he whispered. “I’ve found Flamel! I told you I’d read the name somewhere before, I read it on the train coming here — listen to this: ‘Dumbledore is particularly famous for his defeat of the dark wizard Grindelwald in 1945, for the discovery of the twelve uses of dragon’s blood, and his work on alchemy with his partner, Nicolas Flamel’!”
After this, it plays out how we see it in the film, with Hermoine bringing down her “light reading” and showing it to Harry and Ron.
The ancient study of alchemy is concerned with making the Sorcerer’s Stone, a legendary substance with astonishing powers. The stone will transform any metal into pure gold. It also produces the Elixir of Life, which will make the drinker immortal.
There have been many reports of the Sorcerer’s Stone over the centuries, but the only Stone currently in existence belongs to Mr. Nicolas Flamel, the noted alchemist and opera lover. Mr. Flamel, who celebrated his six hundred and sixty-fifth birthday last year, enjoys a quiet life in Devon with his wife, Perenelle (six hundred and fifty-eight).
Harry is still worried about the Quidditch match and Snape. To make matters worse, Snape is treating him horribly in Potions Class, further enhancing Harry’s fear of him.
Knowing what we do now, most people think Snape hated Harry because he looked so much like his father, and there was conflict between James Potter and Severus Snape. We learn later on that James and his friends bullied Severus pretty severely, so it would be easy to conclude that he hated Harry because of this. I think the opposite is true. I think Severus saw Lily’s eyes in Harry and knew he couldn’t be kind to him or people would suspect his allegiance wasn’t to the Dark Arts.
Ron and Hermione, meanwhile, had found a place in the stands next to Neville, who couldn’t understand why they looked so grim and worried, or why they had both brought their wands to the match. Little did Harry know that Ron and Hermione had been secretly practicing the LegLocker Curse. They’d gotten the idea from Malfoy using it on Neville, and were ready to use it on Snape if he showed any sign of wanting to hurt Harry.
It’s a shame this sequence didn’t make it to the film. There is squabbling between Malfoy and his friends and Harry’s friends, and in the end Harry finds the Snitch quickly and wins the game for Gryffindor. Harry goes to put his broom away after the match and sees Snape sneaking off into the Forbidden Forest while everyone is at dinner. Harry follows him on his broom and sees Snape confronting Professor Quirrell in a clearing. Some of this conversation made it into the film in a different sequence. However, it prompts Harry to tell Ron and Hermoine what he overheard. The three of them figure that Snape is trying to get Quirrell to help him get to the Sorcerer’s Stone.
Previous chapter (link): Harry Potter and the Sorcerer’s (Philosopher’s) Stone Chapter 12: The Mirror of Erised