"School Reunion" is the third episode in the second series of the British science fiction television series Doctor Who. It first aired on 29 April 2006. The episode's narrative takes place some time after the events of "The Christmas Invasion". In the episode's TARDISODE, Mickey Smith alerts the Doctor and Rose Tyler to a comprehensive school where strange things are happening, such as UFO sightings. At the school, the Doctor encounters his former companion Sarah Jane Smith and the robotic dog, K9 Mark III, he sent her, who likewise were interested by the current events. Together, they discover the force behind the events, a race known as the Krillitanes, and work to prevent them gaining control of the universe.