Seven years after the death of his business partner Jacob Marley, a miserable old man named Ebenezer Scrooge is working in his office. He hates happiness, love, family, generosity, Christmas, and probably also puppies. When his nephew Fred invites him over to Christmas dinner, Scrooge yells at him and refuses. Scrooge then tells off the people collecting charity donations, and grumbles and complains that the fact that his clerk Bob Cratchit gets a paid day off for Christmas is theft.
That night, he is haunted by Marley's ghost, which warns Scrooge that the dead who led bad lives are forced to roam around and not be at peace. The ghost also claims that three other ghosts are going to appear to Scrooge, and leaves after telling Scrooge to change his life before it's too late.
Scrooge shakes all this off as indigestion, but sure enough he soon gets a visit from the Ghost of Christmas Past. This spirit takes him on a tour of his childhood memories and Scrooge quickly starts crying when he remembers himself as a neglected boy. The past also features scenes from Scrooge's young adulthood, when he transforms into the greedy miser that he ends up being after rejecting his fiancée and not learning the lessons of hospitality taught by Fezziwig, the man he was apprenticed to.
Now it's time for the Ghost of Christmas Present, which flies him around the country to show how pretty much every other human is making the most of the season by getting together with friends and family. The flyby includes a stop at Fred's house, where a bunch of friends are living it up with dancing and games. Scrooge also gets to check out the dirt-poor but loving Christmas dinner preparations of the Cratchit family. The youngest son is Tiny Tim, a sick, saintly boy.
Next, Scrooge is squired around by a phantom—the Ghost of Christmas Yet to Come. Spoiler alert: Christmas Yet to Come is a pretty sucky place. Tiny Tim is dead, the Cratchits are bankrupt, and also Scrooge himself is dead with no one to mourn him—just a bunch of people to rob his corpse. After seeing his grave and freaking out, Scrooge promises to reform…
… and so he wakes up in his own bed on Christmas Day. He sends a giant turkey to the Cratchits, goes off to Fred's party after all, and gives a honkingly large donation to the charity collector. He changes his attitude and lives the rest of his life with generosity, good cheer, and compassion toward the worse off. Truly, he's become all about the spirit of Christmas. Also he gets a puppy. (Full disclosure: that last part was a lie.)