Desperate for money, the First Church of Springfield plans to rent out its wall space to local advertisers. Horrified at the living commercial the church has become, Lisa withdraws herself from the church and converts to Buddhism.
While watching television, Bart comes across a commercial for a model rocket. Using Homer’s credit card number, he orders one immediately. Soon after, he and Homer are in the backyard trying their luck with the device. Unfortunately, there are several premature explosions, sending them back to the drawing board. Homer is suddenly inspired when Flanders manages a successful launch of his own. Unwilling to be outdone, Homer contacts nerds Doug, Gary and Benjamin and enlists their help in constructing a rocket from scratch. This time, the rocket lifts off majestically and soars into the air. When the rocket veers off-course, Homer contacts the hamster on board, whose name is Nibbles, and relays course correction instructions. But Nibbles bails out, and soon after, the rocket plummets to Earth, where it destroys Reverend Lovejoy’s church. As Homer, Bart and Marge look at the church flames, Marge says to Homer "This is worst thing you have ever done". Homer tells Marge she has said that numerous times and that it has lost its meaning.
With the church destroyed, Lovejoy turns to parishioners for fundraising ideas. Hope comes in the form of Mr. Burns, who asks for permission to run the church like a business. Lovejoy agrees to the idea. The church is rebuilt, but to Lisa’s horror, product displays and advertising are everywhere. The whole family does not mind the changes but during the reading Lisa speaks out about how she hates this. Disgusted, Lisa storms out the door declaring she is leaving the church for good, both of her parents are shocked by this. That night, Lisa prays to God and assures him she has not turned her back on him, but plans to seek a new path to him. Marge however was eavesdropping on her praying and tries to change her mind. Marge tells Lisa she is worried about her soul and wants at least one member of the family to go to heaven. Lisa assures her mother that she still believes in God, she just believes there is another path to him/her. Disillusioned, Lisa begins searching for a new faith. She eventually happens upon Springfield Buddhist Temple. Intrigued, she walks inside, where she discovers Lenny and Carl meditating. She also encounters actor Richard Gere as he rakes a Zen garden. He gives Lisa a pamphlet containing the four noble truths and the path to nirvana. Inspired, Lisa converts to Buddhism. Flanders scared by this goes to the basement with the boys. Word of her conversion also don't sit well with Homer and Marge (although, when Homer appears to be shouting at Lisa he is actually shouting at Bart for not putting butter on his bacon and later for not wrapping it around his sausage). Marge tells Lisa buddhist don't get extra deserts but Lisa tells Marge a buddhist wouldn't want any.
At the church, Reverend Lovejoy turns his attention to the Lisa matter, referring to the girl as “Marge Simpson’s devil daughter.” Lovejoy concludes that Lisa can be wooed back to Christianity by bribing her with Christmas presents. Bart is also taunted by the bullies at school who tell him someone they know is not all right with that. At home Lisa plants a bodi tree and hopes that by meditating under it, she'll find inner peace. Homer tries to help by putting an angel on the tree, Lisa doesn't mind. The next day Marge made Christmas cookies but throws them out because she thinks Buddhists don't believe in Christmas. On Christmas Eve, Lisa discovers a pony named Clip-Clop in the living room. Soon after, Maggie offers her a candy cane. But just as Lisa reaches for the confection, she notices Lovejoy watching her from outside...and urging her to “lick it.” Realizing she’s being bribed, Lisa runs off. The pony turns out to be Milhouse and Ralph posing to form the pony. Later, Lisa visits Richard Gere and tells the celebrity what happened. Gere tells her that Buddhists are free to embrace any faith and celebrate any holiday (as long as it has a kind meaning behind it), including Christmas. Lisa then returns home and sleeps beside the Christmas tree until Marge observes her and celebrates Christmas with the family and when she informs them about her decision, Marge still appears disappointed (calling it lip service to the church) while Homer is satisfied. After asking the whereabouts of her pony, Marge ignores her and continues talking about the new year while Lisa begins to call for Clip-Clop.