As the McCallister family packs for the trip to visit a relative in France, the youngest family member, eight-year-old Kevin, whines about not being able to pack his own suitcase. His siblings pick on him, and things get testy when his brother Buzz devours a pizza set aside for Kevin. Kevin attacks Buzz, causing his mother, Kate, to banish him to the attic bedroom. Kevin grumpily wishes that he didn't have a family and that they would all disappear.
Classic kid drama.
In the morning, the McCallisters leave in a huge hurry (how else would a family vacation start?), and a miscount at the van taking them to the airport causes them to forget about Kevin. Yup, he's still hanging out at home.
The entire family (sans one) is on a plane to France by the time Kevin's mother finally realizes the terrible mistake they've made.
And we thought forgetting our toothbrush was bad.
Meanwhile, Kevin lives it up at home—eating ice cream, watching violent movies, and riding a toboggan down the stairs. It's a kid's fantasy.
He also has to contend with his fear of the basement furnace, and two robbers named Harry and Marv who keep attempting to break-in (Harry posed as a policeman checking in on the family during the movie's first scene, before they left for France). Kevin successfully scares them off, multiple times.
But they're like Wiley E. Coyote—they don't know when to quit. They'll be back.
Building on his newfound self-reliance, Kevin transforms himself into a regular man of the house, even as his mother journeys back from France to make sure he's okay. He even befriends an elderly neighbor who he formerly thought was a serial killer, encouraging the old man (named Marley) to make up with his estranged son.
Kevin's become like Oprah—helping people heal and spreading the love.
Finally, after realizing that he wants his family back, Kevin fends off the burglars as they wander through an intricately violent series of booby traps Kevin's constructed inside the house.
Thanks to the final intervention of Marley—who smashes the burglars over the head with his snow shovel—Kevin survives unscathed, and Harry and Marv are arrested. All is well...except that Kevin's still home alone.
The next day, Kevin's mom makes it home by receiving a lift from a friendly polka bandleader. The rest of the family suddenly shows up, having taken a flight Kevin's mother didn't want to wait for. They're all impressed by Kevin's newfound competence, though he doesn't mention the whole beating-the-pulp-out-of-burglars thing.
The McCallisters get to spend Christmas together, after all. In the end, we also see Marley making up with his estranged son and hugging his granddaughter. Families are getting together all over the place. It's enough to give you a holiday-themed case of the warm fuzzies.