Dorothy is buying a tie for Roger at the department store in preparation for Heaven's Day. Roger snaps at her when he sees her with it. He later apologizes, and soon after that he sees a saxophone player on the sidewalk. He gives him some money. Later, at Roger's house, Norman explains Heaven's Day to Dorothy, one of the traditions being to give presents to those you love. When Dorothy asks Roger if he would be giving gifts to anyone, he becomes nervous and declares that he doesn't like giving gifts. This causes Dorothy to storm out of the room.
Meanwhile, the saxophone player, Oliver, brings home some ham with the money Roger gave him and tells his blind girlfriend Laura that he would like to give her a good Heaven's Day gift.
Elsewhere, Roger consults Norman on Dorothy's reaction and Norman tells him that Dorothy's birthday is apparently on Heaven's Day. Roger asks about Dorothy's dress size and then rushes off to buy her a nice coat, which Oliver is also admiring but can't possibly afford. Oliver gets his pay from his job as a garbage man, realizing that he can't afford a present for Laura. While walking home, he is accosted by a strange character dressed as Santa Claus who gives him an odd bit of jewelry upon recognizing Oliver as playing his sax in the city's center square.
Roger is offered a job by Rosewater, because he has received a threatening card implying danger to the city on Heaven's Day. The card came from a crazy scientist, whose photo shows him to be "Oliver's Santa Claus". Apparently, the scientist believed the world had once been covered in trees and wanted to restore this. While on the job, Dorothy points out that Oliver has a card in his sax case identical to the card received by Rosewater. Roger and Dorothy follow Oliver to his apartment where they talk to him and Laura. Oliver tells Roger that many older people in the neighborhood had the card and had the habit of coming together in a burned out church to sing vaguely remembered songs.
As Roger leaves, Oliver asks if he will buy the jewel from the Santa Claus. Roger harshly declines. The next day (Heaven's Day), Dorothy visits Laura and they talk about love. In the meantime, Oliver is on the street playing his sax, when the jewel cracks open and begins to grow. Soon it explodes out of his pack and carries him up into the air as it becomes a giant tree. Big O saves Oliver and begins to fight the plant. The battle is hopeless and the plant rebounds from all of Big O's assaults. Roger has no choice but to have Norman pick up Dorothy's coat from the tailors. Dorothy brings Laura to the square as the plant stops growing and becomes a giant Christmas tree. Everyone clusters around the tree as Oliver plays Jingle Bells and Roger gives Dorothy her present, only to discover he had been tricked since it wasn't Dorothy's birthday after all. But she also has a present for Roger. Snow begins to fall through the hole created in the dome by the tree and creates a very bucolic scene as the episode ends.