The McCallister family is preparing to spend Christmas in Paris, gathering at Kate and Peter's home in a Chicago suburb on the night before their departure. Kate and Peter's youngest son, Kevin, is ridiculed by his siblings and cousins due to his immaturity. Kevin inadvertently ruins the family dinner after a scuffle with his oldest brother Buzz, resulting in Kate sending him up to the attic. Kevin berates his mother for allowing the rest of the family to pick on him and wishes that his family would disappear. During the night, heavy winds create a power outage, disabling the alarm clocks and causing the family to oversleep. In the confusion and rush to get to the airport, Kevin is accidentally left behind.
Kevin wakes to find the house empty and the family cars still in the garage, unaware that they had rented vans to take them to the airport. Thinking that his wish has come true, he is overjoyed with his newfound freedom. Later, Kevin becomes frightened by his next-door neighbor, "Old Man" Marley, rumored to be a serial killer nicknamed the “South-Bend Shovel Slayer” who murdered his own family. The McCallister home is soon stalked by the "Wet Bandits", Harry and Marv, a pair of burglars who have been breaking into other vacant houses in the neighborhood. Kevin tricks them into thinking that his family is still home, forcing them to postpone their plans to rob the McCallister house.
Kate realizes mid-flight that Kevin was left behind, and upon arrival in Paris, the family discovers that all flights for the next two days are booked, and that the phone lines are still down back home in Chicago. Peter and the rest of the family stay at his brother Rob’s apartment in Paris, while Kate stays at the airport. She fails to find a flight to Chicago, but meets Gus Polinski, the lead member of a traveling polka band, who offers to let her travel with them to Chicago in a moving van on the way to Milwaukee.
On Christmas Eve, Harry and Marv finally realize that only Kevin is in the McCallister home, and Kevin overhears them discussing plans to break into the house that night. Kevin starts to miss his family and asks the local Santa Claus impersonator if he could bring them back for Christmas. He goes to church and watches a choir perform, eventually re-encountering Marley, who proves the rumors about him are false. Marley points out his granddaughter in the choir and mentions he has never met her since she is the daughter of his estranged son. Kevin suggests Marley should reconcile with his son.
Kevin returns home and rigs the house with handmade booby traps. Harry and Marv break in, spring the traps, and suffer various injuries. Kevin calls the police and lures the duo into a vacant neighboring house that they had previously broken into. Harry and Marv ambush Kevin and prepare to get their revenge, but Marley intervenes and knocks them out with his snow shovel. The police arrive and arrest Harry and Marv, having identified all the houses that they broke into due to their habit of flooding them.
On Christmas Day, Kevin is initially disappointed to find that his family is still gone, but Kate arrives home, and they reconcile. The rest of the family then returns after waiting in Paris for a direct flight to Chicago. Kevin keeps silent about his encounter with Harry and Marv, although Peter finds Harry's knocked-out gold tooth. Kevin then happily watches Marley reuniting with his son, daughter-in-law, and granddaughter.
