One year after the events of the first film, and the night before their flight to Miami for Christmas, the McCallister family gathers at the Winnetka, Illinois home of Peter and Kate McCallister. Their son Kevin sees Florida as contradictory to Christmas because he thinks there are no Christmas trees in Florida. During the school Christmas pageant, Kevin’s older brother Buzz humiliates him during his solo, causing Kevin to retaliate and ruin the performance. Kevin refuses to apologize for his actions and is annoyed with his family’s decision to go to Florida, before going up to his third floor bedroom of the house. During the night, Peter unknowingly resets the alarm clock and causes the family to oversleep. In the confusion and rush to reach the airport on time, Kevin boards a flight bound for New York City, carrying Peter’s bag containing his wallet and a large amount of cash; the family is unaware that he is missing until after they land in Miami. In New York, Kevin tours the city and convinces the staff at the Plaza Hotel into giving him a room using Peter’s credit card. During a visit to Central Park, Kevin is frightened by the appearance of a homeless woman tending to pigeons.
On Christmas Eve, Kevin tours the city in a limousine and visits a toy store where he meets its philanthropic owner, Mr. Duncan. Kevin learns that the proceeds from the store’s Christmas sales will be donated to a children’s hospital. Duncan gives Kevin a pair of ceramic turtledoves as a gift, instructing him to give one to another person as a sign of eternal friendship. After encountering the Wet Bandits Harry and Marv (who recently escaped from prison and are now called the Sticky Bandits), Kevin retreats to the hotel. The hotel’s concierge Mr. Hector confronts Kevin about the credit card which has been reported stolen. Kevin flees after evading Mr. Hector, but is captured by Harry and Marv. The duo discuss plans for robbing the toy store that night, before Kevin escapes.
The McCallisters travel to New York after tracking the whereabouts of the stolen credit card and Kate searches the city for Kevin. Meanwhile, Kevin goes to his uncle Rob’s townhouse only to find the house vacant and undergoing renovations while Rob and his family are in Paris. In Central Park, he comes across the pigeon lady. When Kevin gets his foot caught while running away, she frees him. At Carnegie Hall, the pair watch an orchestra perform while Kevin discovers how her life has fallen apart and how she dealt with it by taking care of the pigeons in the park. Kevin vows to the pigeon lady that he will be her friend.
Kevin later returns to the townhouse and rigs it with numerous booby traps. Kevin arrives at the toy store during Harry and Marv’s robbery, throws a brick through the window, setting off the store’s alarm, and leads the pair to the townhouse, springing the traps. When the duo close in on Kevin, he flees the townhouse and calls the police. Harry and Marv are able to catch Kevin and attempt to kill him in Central Park. The pigeon lady incapacitates the duo by throwing birdseed onto them, which attracts the birds and causes them to swarm the crooks, and Kevin sets off fireworks he had bought earlier to signal the police. Shortly afterwards, Harry and Marv are arrested. While at the toy store, Mr. Duncan finds a note from Kevin attached to the brick explaining what happened.
Meanwhile, Kate remembers Kevin’s fondness for Christmas trees. After observing Kevin making a wish at the Rockefeller Center Christmas Tree, Kate meets him there and they reconcile. On Christmas Day, a truckload of gifts arrive at the McCallisters’ hotel room from the toy store. Kevin and Buzz reconcile and Buzz allows him to open up the first present. Kevin goes to Central Park to give the pigeon lady the second turtledove. At the hotel, Buzz receives the bill for Kevin’s stay from Cedric. Peter suddenly calls out, “Kevin, you spent $967 on room service?!”, at which point Kevin runs back to the hotel.