irradiated for at least 25 years. The Silurians re-enter the caves to hibernate until the danger has passed. Since the mechanism is faulty, the younger Silurian will stay awake to operate it and sacrifice his life. The Doctor and Liz repair the reactor. The younger Silurian realises he has been duped into sending his race back to sleep. He attacks the Doctor but is shot by the Brigadier. Later, the Doctor tells Liz that he proposes to revive the Silurians and try to reach a peaceful compromise between them and humanity. However, the Brigadier has other orders, and the Silurian base is blown up. The Doctor is horrified at this act of genocide, but Liz suggests that the Brigadier was acting on orders of his superiors. Production After the previous story, producers Derrick Sherwin and Peter Bryant (who was originally to have the producer's credit on this story) were transferred to the television series Paul Temple, and the BBC intended for Barry Letts to become producer. However, Letts was committed to another production, and could not be released until after the location work on Silurians was completed. Script editor Terrance Dicks and his assistant Trevor Ray shared the production responsibilities for the location work. The incidental music for the serial was composed by Carey Blyton, who would also contribute music for Death to the Daleks (1974) and Revenge of the Cybermen (1975). This story is the first to be recorded using colour studio cameras. The previous serial, Spearhead from Space, was the first in colour, but was shot entirely on location (i.e., outside the electronic TV studio), and on film (as opposed to videotape, the standard method for recording Doctor Who). Due to the move to colour, the production team made use of a technique known as Colour Separation Overlay (CSO, or Chroma key), which allowed images to be superimposed over each other using colour separation. This was used extensively in the series for many years, beginning with this serial. Location filming took place at Marylebone station in London on 12 November 1969, but after the prints were damaged, the scenes were reshot on 24 November after the rest of the serial had been finished. Other location work was undertaken in Surrey, with the heathland scenes filmed at Hankley Common. Alternative titles This was the only time the name "Doctor Who" was used in the title of a serial on-screen