Mork finds himself totally unprepared for earth's Christmas, and perceives that a mind-impairing plague has hit the area. Carolers are singing, Santa Clauses collecting charity give the appearance of martial law enforcing tribute, and people putting plastic babies in straw all add up to an epidemic. But Mork settles down instantly when Mindy explains that it's all part of the Christmas spirit. Humans act human to each other in celebration of the birth of Jesus Christ, the greatest man ever to live on earth.
The superficial Susan Taylor comes to the door. She is bracing to spend Christmas alone. She has received just one Christmas card this year – from her married boyfriend Patrick. She tricks Mork into inviting her to spend Christmas with them, even over Mindy's objections. Furthermore, Susan dictates the festivities by telling them what time to have dinner, what they will eat, and what part of the turkey she is willing to eat.
Eugene comes to the apartment with a Christmas tree, though Mork can't fathom why. As Mork and Eugene discuss Christmas, Susan comes to the apartment with a gift for Mork – a Gucci angel intended to top the tree. Mork perceives the wings to be real, and sends the angel into flight, shattering it as it hits the floor. Susan is undaunted, for she has six more like it at home. One of them is intended for Mindy anyway.
As Susan departs, Eugene tells Mork about giving Christmas gifts, and takes Mork shopping. Mork is frightened by crowded mobs fighting over merchandise, and hides under a display table. The department manager is disinterested when he finds out that Mork intended to purchase four gifts for $12. Eugene explains to Mork that it is perfectly legal to make gifts, and Mork has a plan.
On Christmas Eve, Mork has hidden his gifts, for no one explained how to wrap them. Susan arrives, and Mork becomes overanxious about opening his presents. Mork remembers he has no emotions, and goes up into the attic stoically. When Mindy explains to Susan that his parents never celebrated Christmas, Susan shows the first trace of humanity: she has a lot in common with Mork.
Christmas morning has Mork grooving to Simon music, Cora appreciating a brooch from Fred, Susan liking the gloves from Mindy, and Mindy pretending to like the portrait of Susan. Excitedly, Mork distributes his presents: a piece of carpeting molded into a headpiece, for Fred had wanted a rug; hand-painted bubble gum shaped like Liberace, for Cora loved arts and antiques; a store-bought saucer for Susan, for Mindy advised him to get her something shallow; and a bracelet made of the dead flies that Mindy had been collecting in the attic.
Mork had one more present for the whole house, which he retrieved from the attic. While he was up there, Susan discovers that what she thought was a picture from Patrick was a thousand-dollar bill in a picture frame, and exits to give Patrick a Gucci angel, evidently forgetting her dinner demands. The family discusses how to tell Mork that his gifts were impractical. But Mork overhears them, and dejectedly discards his final gift.
The family comforts Mork, focusing on the thought aspect of his gifts. Then Mork remembers that he can give thoughts as a gift. He gives Mindy a remembrance of her childhood puppy Peppy, whom she had thought was hit by a car, but he returned. He gave Cora a reminder of her first Christmas with her husband. And he gave Fred a memory of the first time he held Mindy.
As they all reach for the Kleenex box to dry their eyes, Mork perceives it snack time, and eats his Kleenex. (There is no report to Orson.)