Plot
Spencer Davenport and his sister Katherine must fly from California to Pennsylvania on Christmas Eve to spend the holidays with their dad. At their layover at the Midwestern Hoover International Airport, a massive blizzard grounds all planes and cancels all flights, and the siblings are sent to the anarchic UM (unaccompanied minor) room, where they meet Christmas-spirited genius Charlie Goldfinch, surly tomboy Donna Malone, arrogant rich girl Grace Conrad, and mysterious Beef Wellington.
Charlie, Spencer, Beef, Grace, and Donna sneak out, and proceed to enjoy themselves around the airport breaking a lot of the rules. Caught by airport security guards and returned to the UM room, they find the other minors, Katherine included, have been sent to a lodge down the road, and that the grouchy head of passenger relations, Oliver Porter – whose trip to Hawaii was also canceled – intends for the kids to spend Christmas Eve in the UM room. Knowing that it will break Katherine's faith in Santa Claus if she does not receive a present by the next morning, Spencer asks the others to help him get a present for her.
With Spencer's plan, the kids give the friendly clerk watching them, Zach Van Bourke, the slip. Mr. Porter grows desperate to get the kids back, so sends all the airport guards to find them. After Donna and Grace get into a fight, Spencer insists they all put their differences aside and work together, and Beef leaves in search of a Christmas tree. Along the way, he reflects on how his stepfather, Ernie, hoped to make him stronger by saying men are made, not born. Meanwhile, Spencer and Katherine's father tries to drive to the airport in his biodiesel fueled car, which breaks down.
The kids head to a thinly secured exit in the back of the airport, distracting the guards by freeing a dog. Attempting to hide from Mr. Porter in the baggage claim, Charlie climbs into a suitcase which gets placed on a conveyor belt; Donna gets on the conveyor belt herself to follow him. Spencer and Grace follow them to the unclaimed baggage warehouse, where they find many presents, including a set of walkie-talkies, and a doll for Katherine.
After seeing the kids on security cameras, Mr. Porter and the guards chase them through the warehouse. Using a canoe, the kids take Zach captive and sled to the lodge while pursued by the guards, eluding Mr. Porter. While on the elevator, Grace has to remove her contact lenses and put on her glasses, to her embarrassment. After they check into the hotel, Spencer & Grace find the hotel room they believe Katherine is staying in, but finds the babysitter, Mary Lynn instead. Mary Lynn refuses to reveal Katherine’s whereabouts Grace frightens away Mary Lynn & Katherine is not in the supposed hotel room. They all congregate to find Katherine asleep in the lobby, and place the doll in her arms.
With their mission completed, the minors quietly go back to the airport with Mr. Porter. He bumps them from their flights and places them under surveillance. The kids then confess why they act the way they do. An emotional Grace admits that even though her parents are still together, they rarely spend time with her and are traveling without her during Christmas. She has just returned from boarding school and chose to stay at the airport instead of going to her nearby home. A sympathetic Spencer devises an escape plan.
Using the walkie-talkies, the minors tamper with the security cameras and escape through air ducts. They find the Christmas decorations Mr. Porter confiscated, and Beef returns with a huge Christmas tree that he had obtained by trading away his prized Aquaman action figure. With Zach's help, the kids decorate the airport, and take items from the unclaimed baggage warehouse to use as presents for the rest of the stranded passengers.
Mr. Porter finds Spencer to admit defeat, and reveals that he is unhappy because he has no family to spend Christmas with and his wife divorced him on Christmas five years ago. Spencer inspires some holiday spirit in him.
On Christmas morning, Mr. Porter dresses up as Santa Claus, hands out presents to the passengers and has the minors' flights restored. Spencer reunites with Katherine, their father arrives to pick them up, Beef tells a girl about his trek to find a Christmas tree, Charlie and Donna exchange phone numbers and kiss, and Grace accepts Spencer's invitation to spend Christmas with him and his family.
