to dominate. He and his followers capture Colby, kill Fendelman, who was actually influenced through his genetics by the Fendahl to bring this about, and set up the Sonic Time scanner to power the skull and Thea's final transformation. The Doctor, Leela, Ma Tyler and her grandson Jack head for the priory only to find the Fendahl core has formed and is converting the cult members into Fendahleen, to form the full circle. The Doctor frees Colby and helps Stael shoot himself after killing one of the new Fendahleen, in turn finding out that they are fatally allergic to salt, leaving the Fendahl core two short of the twelve it needs to be complete and form a gestalt. The Doctor rigs the scanner to implode upon itself and grabs the now dormant skull, leaving with the others only just before the priory is destroyed, along with the Fendahl core and the remaining Fendahleen. The Doctor and Leela then leave and plan to dump the skull near a supernova, thus ending the Fendahl race forever. Production Writer Chris Boucher was commissioned to write the story (his third for the series) on 2 May 1977. He delivered the first episode just two days later, the final one being submitted on the 17 June. Boucher had drawn on the 1967 film (rather than the 1958 TV original) Quatermass and the Pit and the 1959 Kurt Vonnegut novel The Sirens of Titan including the discovering of an alien skull linked to occult symbols, alien influence of mankind's evolution and the dormant alien influence being brought to bear in contemporary humanity. He also took inspiration from the work of archaeologist Louis Leakey who had been excavating human remains for many years until his death in 1972. Boucher named Colby's dog Leakey as a tribute to him, although later realised that people would miss the reference and assume the name came because "he pissed all over everything!" Terrance Dicks' subsequent novelisation of the serial in fact gives both reasons for the name. At the initial read through Tom Baker made numerous jokes about the script, picking out all the double entendres and sending it up. This caused Boucher great upset at the time, but had the knock-on effect of him combing through his scripts from there on for any signs of double entendres. Boucher never wrote for the series again, immediately after this becoming script editor