The Sontaran Experiment
Starring: Tom Baker (The Fourth Doctor), Elisabeth Sladen (Sarah Jane Smith), Ian Marter (Surgeon-Lieutenant Harry Sullivan).
The Doctor agrees to transmat down to Earth to make sure everything is okay before the Nerva survivors begin to reclaim their planet. There, he, Sarah Jane and Harry discover the presence of a Sontaran named Styre, who is performing cruel experiments on a band of captive humans. Styre's goal is to discover the weaknesses of the human body -- weaknesses the Sontarans will then exploit in their quest to dominate the universe.
For much of the Seventies, the usual Doctor Who season had been a virtually exclusive mix of four- and six-part stories. New script editor Robert Holmes was not a fan of the latter, however, feeling they were often padded out. Amongst the stories for Season Twelve already commissioned by the time he took over was Space Station by Christopher Langley. By Spring 1974, it was evident that Langley's story was not working out (it was formally rejected on June 17th), and to replace it, Holmes and new producer Philip Hinchcliffe decided to commission not one but two stories, one a two-parter and the other a four-parter. The former would be made entirely on location and the latter would be confined to the studio, meaning the two productions would not take up more resources than a six-episode story. This would be the first time Doctor Who had essayed the two-episode format since The Rescue in 1965.
To write the two-part story, Holmes contacted veteran Doctor Who writers Bob Baker and Dave Martin, whose most recent contribution had been The Three Doctors two seasons earlier. Holmes wanted to tie the two new stories together, and so gave the Bristol Boys an idea from which to work. The duo was commissioned to flesh out the storyline on May 23rd, and to write part one on June 5th; by this time the serial had earned the title The Destructors. Later, in August, Holmes went back and inserted references into the script to the four-part story, The Ark In Space, which would be made after The Destructors but aired first. The only major alteration from script to screen was the movement of the action from a ruined town to a rocky landscape when a suitable location couldn't be found. Holmes specifically requested that Baker and Martin include a single Sontaran in The Destructors, since reusing the Lynx costume (from the previous season's The Time Warrior) from storage would be a cost savings. In the event, however, a new more lightweight costume was constructed since it was now known that actor Kevin Lindsay suffered from a serious heart condition (he would die of it just six months later).
By the time taping began, the serial's title had been changed to The Sontaran Experiment, much to the dismay of the writers who felt this spoiled the episode one cliffhanger. All the material was recorded on location in Dartmoor under the aegis of director Rodney Bennett (who would continue on to helm The Ark In Space), making his first Doctor Who story. Amongst the cast was Glyn Jones playing Krans; Jones had written The Space Museum for Doctor Who's third season. Recording began on September 26th and proceeded without undue delay until the 28th. On this day, while filming the Doctor's confrontation with Styre before a captive Sarah, Tom Baker slipped and fell on the rocks. He had to be carried back to the nearest car and driven to the hospital, where it was discovered he had cracked his collarbone. Baker was able to finish the shoot by wearing a neck brace concealed beneath his scarf and coat, but was forced to remain very still as a result. The final scenes for The Sontaran Experiment were recorded on October 1st.