It's Christmas, and there is so much to do, especially when your entire family is going on vacation. The McCallister family is headed to Paris to spend Christmas with family. Bratty eight year old Kevin McCallister (Macauley Culkin) gets into an argument with his older brother, Buzz, and is sent to bed early, wishing that his family would just disappear. Well, that's the thing about Christmas wishes - they have a magical tendency to come true. That night there is a power outage which re-sets all the appliances in the house, including the alarm clocks, which do not go off as planned. The family is left scrambling to make it to the airport in time to catch their flight accidentally leaving Kevin behind. His absence is not noticed until the plane is airborne, leaving his frantic parents trying desperately to book a flight home again as soon as they deplane in France.
Meanwhile, back at the McCallister home, Kevin thinks that his Christmas wish has come true when he realizes he is alone in the house. He does all of the things he is never allowed to do - bounces on the beds, uses Buzz's BB gun and eats junk food whilst watching gangster movies. However, he is also a little scared by Old Man Marley who lives next door because local myth tells it that the old man murdered his entire family years before; the appearance of him outside his house with a shovel makes Kevin very nervous. Then there is the matter of the Wet Bandits, Hal and Marv, who are in the middle of an inept, but determined, crime spree and are breaking into houses whilst people are away for the holidays.
Kevin overhears the bandits talking about breaking into the McCallister home on Christmas Eve, and as the man of the house in the absence of his father, he decides to stymie their efforts. He also runs into Old Man Marley watching a local choir performing in the church; they talk, and Kevin learns that the old man is actually very nice. He is watching the choir because his granddaughter is in it, and he doesn't get to see her anymore because he and his son had a big argument and no longer talk. Kevin advises him to reconcile with his son so that he can spend Christmas with his family. Kevin heads home after church and prepares to booby trap the house so that the bandits cannot break into it. He sprinkles broken tree ornaments that are made of glass underneath the windowsill so that when the men break in they will cut their feet; he also booby traps the cellar, causing Hal to break a tooth when a can of paint hits him in the face. They chase Kevin through the house and hang him on the towel hook behind the bathroom door when they catch him but he has already called 911. Kevin escapes the house with the burglars in hot pursuit, but Old Man Marley comes up behind them, knocking them out with a swing of his snow shovel, and taking Kevin home. The police arrive, and the burglars are arrested.
Kevin wakes up on Christmas morning hoping that his family will be home, but they are not, but he hears his mother open the front door and call his name. Kate McCallister has driven home with a performing band, squished tightly into the back of their RV, and is relieved to see her son again. Soon afterwards, the rest of the family, fresh from their flight from Paris, arrive. Even Buzz is pleased to see him. Kevin does not tell his family about his encounter with the Wet Bandits, but when his father finds the burglar's gold tooth on the floor he wonders what could be. Kevin sees Old Man Marley out of the window and sees that he has invited his son and the family over for Christmas; he watches as they reconcile and the old man greets his beloved granddaughter. The idyllic picture is interrupted as Buzz yells out to Kevin about the state of his room.
