Sarah Jane Smith continues to live her life on Bannerman Road. Investigating a nanotechnology company, she is thrown out and goes back to her house, when suddenly, an alien space pod crashes into a building. Sarah Jane and the gang take a trip to the building, where Judoon Captain Tybo is shooting at an alien escaped prisoner, Androvax, a Veil, who soon possesses a little girl. Luke and Rani team up with the Judoon Captain, while Sarah Jane and Clyde meet the little girl. Sarah Jane becomes possessed and Clyde is put out of focus. Luke, Rani and Captain Tybo locate him and he is awakened.
Meanwhile Gita and Haresh pay a visit to the nanotech company to help improve Gita's flower business but they are arrested. The Judoon Captain, Clyde, Luke and Rani arrive at Bannerman Road to discover that the possessed Sarah Jane Smith has ordered Mr Smith to self destruct with a one minute countdown.
Luke talks Mr Smith out of self destructing ; the team heads over to the nanotechnology laboratory to save Sarah Jane and for Captain Tybo to bring in Androvax who must be executed for the destruction of 12 planets. The evil Sarah Jane Smith has released the nanoforms, to build a spacecraft for Androvax, threatening to destroy the Earth in the process. Gita and Haresh are arrested by the guards. They easily escape and are then confronted, scanned and catalogued by newly arrived Judoon troopers. Androvax/Evil Sarah Jane explains that the spaceship design is based on the crashed Roswell spaceship, and then reveals that he wants to destroy everything, since he was upset when his planet's sun burnt out and wants to destroy all inhabited worlds believing that destruction is the way of the Universe.
Clyde and Rani use a ruse to lock Captain Tybo in a lab room and use fire extinguishers to freeze the nanobots which were eating through a door. The troopers free Captain Tybo and then everybody converge in the now completed spaceship control room where Androvax is arrested by the Judoon platoon. Luke uses the ship's controls to deactivate the nanobots. The Judoon charge Clyde and Rani with interference, but take the pair's assistance and motives as mitigating factors, limiting their punishment to a bar to extraterrestrial travel. The Judoon leave with their prisoner, and the gang as well as Gita and Haresh — who have not seen that their daughter and her friends were involved in the events they have witnessed — return to Bannerman Road. Gita and Haresh are left in shock to have seen real aliens.