guards who are in turn responsible to two robots called Seers. In overall control is the Oracle, a powerful super-computer which has shaped the perverse society. Evidently the P7E became trapped in the planet millennia earlier and the entire basis of the mission was lost over time. The Doctor and Leela encounter Idas, a young man nearly killed in a Skyfall, learning how the local population is managed and terrorised. The Seers and Oracle exist in a protected Citadel at the heart of the planetoid (clearly the P7E) and the Doctor, Leela and Idas venture there, in the process rescuing Idas’ father Idmon who was due to be sacrificed to the Oracle. Other slaves are freed too, and flee to the R1C where Jackson makes them welcome. However, the crucial race banks remain in the control of the Oracle. The Doctor, Leela, and Idas venture to the Citadel to get the precious cargo. However, the Seers have meanwhile captured Herrick and give him what he thinks are the two race banks to take back to his ship. Jackson, Orfe and Tala are overjoyed, little realising that their friend has actually brought fission bombs back to the R1C. The Doctor makes it to the core of the Citadel and confronts the Oracle. He succeeds in locating and stealing the real race banks and then heads off with Leela and Idas to get back to the probe ship. The Doctor gives the real race banks to Jackson, and then takes the fakes out of the craft. Idas takes advantage of the situation to round up the other Trogs and lead them to the safety of the R1C, while the Doctor engineers the return of the fission grenades to the Oracle. With moments to spare, the R1C blasts away, loaded with the slaves and the race banks, and is pushed outward from the planetoid by the explosion of the fission grenades. The TARDIS crew depart, wishing the Minyans well as they journey on to Minyos II, their quest complete. Production Underworld was recorded entirely in-studio in October 1977. In an attempt to save money on production costs, the serial was recorded using the Colour Separation Overlay (CSO) technique. This approach involves recording the actors against a bluescreen, and then superimposing them on models of the sets – thus saving on the costs involved in set construction. Background The serial borrows many elements and