The Whos down in Whoville are preparing for Christmas; trimming trees, hanging wreaths, and wrapping presents. Meanwhile, the Grinch watches from his cave in the mountain above. He reviews the Whos' plans for celebration, including playing games, singing, and dining upon roast beast - all things that the Grinch despises. He decides he needs to stop Christmas from coming, and ponders strategems for doing so.
Eventually he comes up with an idea. He sews himself a Santa Claus hat and coat, and outfits his dog Max with a horn to make him look like a reindeer. He loads some bags onto an old sled and has Max pull it down to the village.
Climbing down an inhabitant's chimney, he steals the stockings, the presents, and the tree, even stealing candy canes away from sleeping children. He steals the roast beast and other food from the icebox. Inadvertently he wakes the child Cindy Lou Who, who, mistaking the Grinch for Santa Claus, asks him why he is taking the tree. The Grinch tells her he is repairing the tree and puts her back in bed. Finally he takes the log for the fire. He then treats each house in the village similarly.
He retreats to his mountain with the spoils, planning on dumping them all into a ravine. But before he does so, he pauses to listen to the village, in hopes of hearing the Whos crying. Instead, he hears singing. He realizes that Christmas had come regardless of the lack of material goods.
The Grinch has a change of heart. He recovers the sled just before it can slide into the ravine, and slides back to the village to return the goods. The Grinch is welcomed back and himself carves the roast beast at the celebration.