After colliding with a spaceship, The Doctor, Romana and K-9 learn young natives from a peaceful planet called Aneth are being transported into a great labyrinth called "The Power Complex" where the evil bull-like Nimon demands that all his victims who enter The Power Complex are sacrificed so The Nimon can return to the Skonnan Empire back to glory. When Romana is taken captive and also chosen for sacrifice, The Doctor and K-9 travel to the heart of the maze as they set out to rescue Romana and foil The Nimon's evil plan to enslave the universe.