In 1996, Prisoner Zero was a captive in an Atraxi extra-dimensional prison. When a crack in the universe opened into Amelia Pond's bedroom wall, Prisoner Zero escaped through to Amelia's house in Leadworth. It hid in a room in Amelia's house, placing a perception filter on the room's door so it would not be found. It hid on Earth for twelve years, watching Amelia grow up. It sometimes ventured into the village, posing as comatose people in Royal Leadworth Hospital whom it had established a psychic link with, a process that took months. If the person it was copying was dreaming about having someone else with them, Prisoner Zero would appear to be multiple lifeforms touching each other. It was actually one creature with many limbs and orifices.