It's winter in Who-ville as Old Max the dog enters, and carolers sing in the distance ("Opening"). Turning to the audience, he begins to reminisce about "that hole in the mountain" where he used to live.

The scene takes us back many years ago,. The citizens of Who-ville excitedly prepare for Christmas ("Who Likes Christmas?"). But who doesn't like Christmas? The Grinch, who lives on the mountain north of Who-ville with Young Max ("This Time of Year"). In his cave, the Grinch declares his contempt for the Whos in Who-ville and all things related to Christmas ("I Hate Christmas Eve"). Meanwhile, the Who family wraps presents in their home. Cindy-Lou Who suggests giving the Grinch a Christmas gift, but the Adult Whos tell her it's no use.

The Grinch drives himself into a frenzy as he imagines the delighted Who-Kids discovering their gifts ("Whatchamawho") and singing carols ("Welcome, Christmas"). Young Max is moved by this vision while the Grinch is enraged. He devises a plot to stop Christmas ("I Hate Christmas Eve (Reprise)").

In Downtown Who-ville, Mama Who and the rest of the Who family are shopping for gifts. Cindy-Lou points to a red rocking horse that she wants for her gift. Papa Who finds it all very overwhelming, but the family reminds themselves that "It's The Thought That Counts". The Grinch sneaks around town in disguise to buy supplies for his plot. When he runs into the Who family, he pretends to be a tourist. Papa Who invites him to their Who-sing and Christmas feast. The Grinch says he might take them up on the offer and runs off.

Back in the cave, Young Max wears fake antlers for the Grinch's plot ("This Time of Year (Reprise 1)"). The Grinch reveals the Santa suit he made for himself ("One of a Kind"). The Grinch rides off in a sleigh, driven by Young Max.

After tucking the children in, the Adult Whos await the coming of Christmas morning ("Now's The Time"). When the coast is clear, the Grinch sneaks into the house and steals their food, presents, and even their Christmas tree ("You're a Mean One, Mister Grinch"). Cindy-Lou catches him in the act and, believing he's "Santy Claus", asks why he's taking their tree. The Grinch promises he'll bring it back in the morning. A tearful Cindy-Lou hugs him - a gesture the Grinch is unfamiliar with. She begs him to stay the night and is saddened to learn that "Santy" spends Christmas alone ("Santa for a Day").

The Grinch continues his stealing spree around Who-ville ("You're a Mean One, Mister Grinch (Reprise)"). On Christmas morning, the Whos awake to find their living room ransacked and all their Christmas gifts, decorations, and food gone. The Grinch is excited to hear their disappointment, only for the Who family to affirm that friends and family are the most important part of Christmas ("Who Likes Christmas (Reprise)"). The Grinch is moved and has a complete change of heart ("One of a Kind (Reprise)"). With Young Max, he heads off to return everything he stole.

Old Max tells the audience that he always remembers the Grinch's miraculous transformation during "This Time of Year (Reprise)".

The Whos of Who-ville gather to sing ("Welcome, Christmas (Reprise)"). To everyone's surprise, the Grinch joins them! With encouragement from Young Max, he wishes them a Merry Christmas and gives back their gifts, including the red rocking horse for Cindy-Lou. She tells the Grinch that there's only one thing missing from their Christmas celebration - him. ("Finale")