discovers a covert listening device in his room. He imprisons Garron with his "accomplices", the Doctor and Romana, and starts the search for Unstoffe, who still has the money and the jethrik. Unstoffe hides with Binro, a homeless outcast who believes that Ribos is a planet orbiting a star, and that there are other stars in the universe, which Unstoffe confirms to be true (because he was from Earth). The Ribos guards summon a Seeker who locates Unstoffe's hideout. Using the listening device in the Graff's room, Garron warns Unstoffe about the Graff. Binro, thankful for Unstoffe's encouragement, leads him to the labyrinthine Catacombs under the city, where the natives bury their dead. The Graff and his men enter the Catacombs without the guards, who fear the place, and the Seeker warns that if they enter, "All but one are doomed to die." K9 helps the Doctor, Romana, and Garron escape and go to the Catacombs. The guards destroy the entrance to the Catacombs causing the ceiling to collapse on the Graff's men. Having recovered the money and the jethrik, the Graff gives his last surviving guard an explosive to kill himself with. The guard, actually the Doctor in disguise, swaps the explosive for the jethrik. The Graff walks off into the maze yelling like a madman as the sounds of one of his previous battles resound around him, before exploding. After leaving the Catacombs, the Doctor, Romana, and K9 dematerialise in the TARDIS. Garron and Unstoffe claim the Graff's deserted ship, full of years of plunder, while the Doctor and Romana transform the jethrik into the first piece of the Key to Time. Production Working titles for this story include Operation and The Ribos File. The opening scene, with the White Guardian, was actually written by Anthony Read and Graham Williams, and not Robert Holmes. The serial was filmed entirely in studio in April 1978. From this story until The Horns of Nimon (1979–80), Baker wears an extra-long scarf, which is the original scarf and the stunt scarf sewn together. Cast notes Elisabeth Sladen, who as Sarah Jane Smith was last seen in The Hand of Fear (1976), was approached to return to the series as a replacement for Leela (who had left in The Invasion of Time). When Sladen declined the offer, Romana was created. Prentis Hancock had appeared in Spearhead from Space (1970), Planet of the Daleks