The film was previously titled They Came from Upstairs, which is instead used as the film's tag line. A video game of the same name was released as well.
A meteor shower rockets through open space. Four glowing pods are seen hiding behind the meteor shower. Suddenly the meteor shower makes a hard right and heads towards a distant planet Earth.
In a Chicago suburb, Stuart Pearson and his wife Nina head a family that includes 7-year-old Hannah, 17-year-old sister Bethany, who has just come back from a secret outing with her boyfriend Ricky Dillman, and 15-year-old techno-geek Tom whose high school grades are low. Deciding the family needs some good old-fashioned togetherness, Stuart takes them to a holiday home in the middle of nowhere. Joining them is Uncle Nate, Nate's 14-year-old son Jake, Nana Rose, and identical 12-year-old twins Art and Lee. Ricky also arrives unexpectedly and talks his way into staying overnight.
That night dark storm clouds swirl around the house. Suddenly, the four glowing pods land on the roof. An alien crew emerges, made up of Skip, the tough commander, Tazer, a muscle-bound dude armed to the teeth, Razor, a lethal female alien soldier, and Sparks, a four-armed techie, who is the only non-threatening intruder. Since the aliens knocked over the satellite dish Ricky and Tom are sent to fix it. Ricky then reveals to Tom that he lied about his car breaking down, and his age; Ricky is actually in college and is 21 years old, five years older than Bethany. Ricky makes Tom fix the satellite dish by himself but it is beyond repair. Investigating further, Tom and Jake (who unexpectedly shows up on the roof) discover the aliens. Ricky is captured and implanted with a mind control device. The aliens, called "Zirkonians", lay claim to the planet. Like a puppet, Ricky grabs the boys – but Tom and Jake break free and get back in the house.
It is not long before all five kids have seen the aliens, with the exception of Bethany. Tom takes charge and they discover the mind control device doesn't work on children, giving them a fighting chance. They realize they have a responsibility to protect the adults by keeping the aliens' existence a secret. The kids create makeshift weapons, like a homemade potato spud gun. They repel the first alien attack from the attic and obtain Ricky's remote control and turn him against the aliens.
The kids orchestrate a scheme to get the adults out of the house and then ambush the aliens as they try to reach the basement, causing the gentle tech Sparks to become separated. He meets Hannah and they become friends. Unlike his alien cohorts, Sparks hates battle; he just wants to return home to his family, and he helps by making weapons for them. He also reveals the aliens want a device hidden under the basement which will make them grow giant. The kids forgot about their grandmother, and the aliens mind control her, which gives her superhuman strength and agility, and she fights with Ricky in a scene reminiscent of a fighting video game. However, the aliens manage to capture Jake and hold him hostage in exchange for Sparks, whom they need to complete their mission.
The kids finally reveal to Bethany what's going on. Ricky then breaks up with Bethany because she always talks about feelings and family and leaves. The five of them rescue Jake, but Skip succeeds in using the enlarging machine and calls the Zirkonian invasion ships. They defeat him and shrink him again. Tazer and Razor flee, while Skip is shrunk to a tiny size by the machine. Sparks calls off the invasion and returns home. The rest of the vacation goes back to normal, except the kids grew closer to each other during their adventure. In the distance, Skip appears, bent on revenge, but meets his demise when a crow flies over and grabs him.
In a mid-credits scene, Bethany and Tom take revenge on Ricky by making him look like a fool in front of his new girlfriend, using the alien mind control device. Bethany comments "I am so keeping this".
- Carter Jenkins as Tom Pearson
- Austin Butler as Jake Pearson
- Henri Young as Art Pearson
- Regan Young as Lee Pearson
- Ashley Boettcher as Hannah Pearson
- Ashley Tisdale as Bethany Pearson
- Robert Hoffman as Ricky Dillman
- Kevin Nealon as Stuart Pearson
- Gillian Vigman as Nina Pearson
- Doris Roberts as Nana Pearson
- Tim Meadows as Sheriff Doug Armstrong
- Andy Richter as Nathan Pearson
- Malese Jow as Julie