It's a day before the McAllisters, a large family, go on holiday in Paris. Kevin, the 8-year-old, is despised by everyone else. His mum sends him up to the attic bedroom the night before. The next morning, they leave, forgetting to take him with them, and they don't realise until they are halfway across the Atlantic!
When Kevin discovers he has the large house to himself, he has the time of his life, but he is afraid of the neighbour, an old bearded man. Also, two burglars are determined to break in. Kevin pretends to have a party to scare them away one night, another time he lets firecrackers off in the kitchen. Finally, the burglars do get into the house, but Kevin has filled it with booby traps, which see the crooks being burned and banged on the head, among other things.