the drilling stopped, but like in the other reality his warnings are ignored. This time, however, the slower pace of the drilling means that Stahlman fully transforms into a Primord before the crust is penetrated instead of afterwards, and after the Doctor kills him with a fire extinguisher, the drilling is stopped in time to prevent disaster. Satisfied that the TARDIS console is now working again, the Doctor attempts to depart, only to end up landing in a local rubbish dump. Production Scriptwriter Don Houghton was a personal friend of the Doctor Who script editor, Terrance Dicks: they had worked together for Lew Grade at ATV in the 1960s, on the TV soap opera Crossroads. During a train journey, Houghton discussed with Dicks his idea for a serial based on the real life drilling project known as Project Mohole. Budgetary limitations eventually led to the concept of the parallel world, so that the same actors and sets could be used for seven episodes, rather than the four episodes in Houghton's original story breakdown, in order to cut costs. Despite Douglas Camfield receiving sole credit as director, the studio scenes for episodes 3 to 7 were directed by producer Barry Letts after Camfield had a minor heart attack on April 27, 1970. Letts later stated that Camfield's preparations were so meticulous, he merely followed Camfield's plans for Episodes 3 and 4, but the latter three episodes were largely his own work. Camfield remained credited as director, as BBC regulations at the time forbade Letts from being credited for more than one production role (i.e. as both producer and as director), but, more importantly, Letts did not want Camfield's illness to become widely known lest it harm his career. Stuntman Derek Ware did not actually perform the stunt in which his character, the mutated RSF Trooper Wyatt, having been shot, falls to his death from the top of one of the chemical tanks, in case he was injured (since he was also needed for the subsequent studio recording). His place was taken by Roy Scammell, who (ironically) also played the soldier who fired the fatal shot. Ware stated in an interview that Scammell had already signed the contract to do the fall before Ware had been cast as Wyatt. At the time it was filmed, it was the highest fall ever performed by a British stuntman. John Levene's portrayal of Benton as