Harry realizes that Hagrid's dragon acquisition seems pre-tty suspicious.
The three descend upon Hargid's hut and put the final pieces together: the dog is guarding the Sorcerer's Stone.
They ask Professor McGonagall to let them talk to Dumbledore, but he's gone.
The kids tell her that the Sorcerer's Stone is in danger, and she brushes them off.
They run into Snape, who menaces them for being indoors on such a beautiful day.
The three set out after dark to find the Stone.
Neville Longbottom, one of their fellow Gryffindors, tries to stop them, and Hermione paralyzes him with a spell.
When the three arrive at the dog's chamber, they discover that someone's arrived just before them. A magic harp is keeping the dog asleep.
The trio move towards the trap door, but the dog wakes up before they can get there, and sends them all crashing into Devil's Snares: a pack of strangling vines.
Hermione, smart cookie that she is, knows how to defeat the plants—by totally relaxing—and helps Ron and Harry through it.
The next room holds a different test: a magic flying key to a locked door blocking their passage, zipping around amid a host of others.
Harry hops on a convenient broomstick and snags the key before the other keys cut him to ribbons.
Beyond the door sits a life-sized game of Wizard's Chess.
The trio play is out, as living piece, under Ron's direction. Ron sacrifices himself so that Harry checkmates the king.
Harry moves on alone into the final chamber.
He discovers Professor Quirrell in front of the Mirror of Erised.
Quirrell explains that he was the one trying to knock Harry off his broom during the Quidditch match; Snape had interfered.
Quirrell and a second voice command Harry to gaze into the mirror.
He sees his reflection discovering the Stone in his pocket, and miraculously, Harry finds the Stone in his own actual pocket.
When Quirrell demands to know what Harry sees, Harry lies, and the strange voice knows it.
Quirrell reveals that he's host to Voldemort's parasitic spirit: manifesting as a face on the back of Quirrell's skull. (We know…ick.)
Voldemort attempts to seduce Harry to join him in exchange for the Stone in his possession.
Harry refuses and Voldemort orders Quirrell to kill him.
Harry somehow manages to inflict deadly harm on Quirrell with his touch.
With the destruction of the vessel, the remaining essence of Voldemort is left formless again, and it flees in anger and defeat.
Harry passes out, then wakes up in the hospital wing with a tray of candies and gifts from friends and admirers.
Dumbledore fills the gaps in for us—Ron and Hermione are fine, and the Stone appeared in Harry's pocket thanks to an enchantment of Dumbledore's—before revealing that the defeat of Voldemort is merely temporary.
Harry, Ron, and Hermione are united again, a bit bruised up, but happy to see each other.
Dumbledore stands in front of a filled Great Hall for the final feast of the year.
The end of the year points are tallied, and to absolutely no one's surprise, Gryffindor manages to pull a win for the House Cup thanks to the actions of the previous night. (Even Neville gets some recognition for standing up and getting himself petrified.)
Hagrid joins the kids on the train platform to say goodbye.
He gives Harry a photo album of his parents, and a giant hug.
The kids climb aboard, and the train pulls out of the station, back to London.