The Sontaran Experiment ( TV story ) The Sontaran Experiment was the third story in the twelfth season of " Doctor Who " . Shot entirely on location , it was the shortest story of the 1970s , with only two episodes . An outdoor shoot , all scenes were surprisingly recorded on videotape rather than film . Script editor Robert Holmes was not a fan of six - part stories , believing that they were padded , so for season twelve , he decided to have one four - part story and one two - part story . With Christopher Langley ' s " " Space Station " " already in the works , he looked to Bob Baker and Dave Martin to fill the gap . As an outline , Holmes asked them to set it on Earth and bring back the Sontaran s . This would help them capitalise on the costly ship interior and Sontaran costume used in " The Time Warrior " . Baker and Martin were commissioned to write the script on 23 May and asked to deliver episode one shortly after , on 5 June . Part two was in by 6 July and Holmes re - wrote it extensively , removing a sub - plot in which Vural was revealed to be a victim of mind - control . Despite Holmes ' earlier intentions , a new Sontaran costume was made for Kevin Lindsay . The previous one had exacerbated his heart condition , an illness that killed him six months later . Synopsis . Arriving on a seemingly deserted Earth , the Doctor , Sarah and Harry soon discover a crew of shipwrecked astronauts from a distant Earth colony . Lured there by a fake distress call , the astronauts are being experimented on by the deadly Sontarans in preparation of a full - scale invasion of the planet . Can the Doctor defeat Sontaran Field - Marshall Styre and save the world ? Plot . Part 1 . The Fourth Doctor and his companions Sarah Jane Smith and Harry Sullivan transmat down from Space Station Nerva to a field on the now - healed Earth . The Doctor starts fixing the circle of transmat refractors with his sonic screwdriver while the others wander off to explore . As they walk across the plain , Sarah hears a sound and sees movement on the top of a hill . Harry dismisses it . Two men in spacesuits , Erak and Zake , are observing the Doctor through the crosshairs of their rifles . Erak leaves Zake to watch the Doctor while he reports the presence of the Doctor to another man in a spacesuit , Krans , who is tending a campfire . Meanwhile , Harry slips on the edge of a hole and tumbles into it . He is stuck , unable to climb out . Sarah observes that the edge of the hole had been covered deliberately . Harry has no choice but to stay put as Sarah goes to fetch the Doctor . Zake ' s observation of the Time Lord is interrupted by a strange floating robot that bears down on him . Zake flees , the robot pursuing him over the edge of a cliff . The Doctor finds Zake ' s body when Erak and Krans arrive . Thinking the Doctor has killed Zake , they stun him with their rifles before he can explain . As they carry the unconscious Doctor away , they are watched by yet another spaceman , Roth . Sarah gets back to the circle to find the Doctor gone , his screwdriver abandoned . When Sarah returns to the hole , Harry is nowhere to be seen . Something had started throwing rocks down at Harry and , in scrambling for cover , he found a way out of the hole , climbing through some rocks to the hills beyond . Sarah is about to climb down into the hole to look for Harry when Roth grabs her from behind , hiding her as the drone floats past . Once the danger is gone , Roth introduces himself to Sarah . It was he who covered the edge of the hole , trying to trap the drone . He tells Sarah that the robot serves an alien who lives among the rocks , an alien who has tortured him and killed two of his crew . Roth is obviously traumatised by his experiences . He vows he will not be captured again . When Sarah tells him about her friends , he informs her that the Doctor has been taken to the campsite . At the campsite , Erak and Krans interrogate the Doctor , demanding to know what he has done to their crewmates . When the Doctor explains that he came down from Space Station Nerva , the spacemen ( now joined by their leader , Vural ) greet that news with great scepticism . Nerva , the lost colony of mankind , is a mere legend , like Atlantis . The spacemen are from one of the colonies , GalSec . The Doctor suddenly spots an odd looking button on Vural ' s suit , identifying it as non - human technology . The button is actually a remote camera . Somewhere else , everything is being observed by something with a grey , heavy , four - fingered hand . Roth brings Sarah near the campsite but refuses to approach ; he tells Sarah he saw Vural go to the rocks and the alien let Vural go . The GalSec men tell the Doctor that a GalSec freighter had gone missing . Detecting a distress signal from the supposedly uninhabited Earth , they came to investigate , but their ship was vaporised when they emerged , leaving nine of them stranded . The surviving crew began to vanish one by one . The Doctor offers to fix the transmat refractors and beam them all to Nerva , where they can contact another GalSec ship , but Vural says that they are not taking orders from the " Old People " . While the Nervans did nothing but sleep , the rest of mankind had spread across the galaxy and built an empire . At this point , Roth appears . While the three spacemen chase him , Sarah sneaks out from the rocks and frees the Doctor . Roth loses the others and meets up with Sarah and the Doctor . Sarah tells the Doctor about the robot , and the Doctor examines some residue on the ground , evidence of a terullian drive , except there is no terullian in this galaxy . The Doctor reasons that there must be some way out of the hole that Harry fell in , but as he climbs down , he too slips and falls to the bottom , losing consciousness . At that moment , the robot returns and snares Roth and Sarah with cables . Harry has made it to the hills , where he spots a man - sized metal sphere among the rocks . As he watches , the robot arrives with Roth and Sarah in tow . The sphere ' s door opens and to Sarah ' s horror , out steps a Sontaran warrior . Part 2 . When Sarah expresses her disbelief , the Sontaran tells her he is Field Major Styre of the Sontaran G3 Military Assessment Survey , identical to the other Sontaran clone she encountered , but not the same . Roth cries out that he will not be tortured again and makes a break for it , only for Styre to shoot him down . Roth had already been tested , so he was of no further use . Sarah , however , is far more interesting . The three spacemen find the Doctor in the hole , but as they force him to climb out at gunpoint , the drone arrives and snares the trio . The Doctor goes back to the bottom of the hole . He finds the same exit that Harry used . Harry , in the meantime , finds another human chained to the side of the rocks , severely dehydrated . Nearby , Styre has Sarah tied up to the rocks as well and has placed a device on her forehead . He seals her in with a force field . Styre goes to his transmitter station and reports to his Marshal . The Marshal is impatient for the intelligence report , but Styre tells him that some inconsistencies have arisen that he has to clear up before he submits it . Styre proceeds to subject Sarah to Experiment 7 : resistance to fear . The device on her head begins to give Sarah hallucination s , and she starts to panic . The Doctor , however , has reached her and uses the sonic screwdriver to breach the force field . When he rips off the device on her forehead , she gives a scream and falls unconscious . The Doctor , enraged , attacks Styre , but the Sontaran easily fends him off . Styre shoots him when he runs , the Doctor collapsing in a heap . Harry finds Sarah , unconscious , and the Doctor ' s apparently lifeless body . The chained - up spaceman has also died of thirst and Styre records the result of Experiment 5 : human resistance to fluid deprivation . Harry prepares to attack Styre from behind but is dragged back by the Doctor . Styre ' s shot had hit a piece of scrap metal the Doctor had taken from Nerva , saving his life . The Doctor tells Harry to look after Sarah while he discovers Styre ' s mission . The robot brings the three remaining spacemen to Styre ' s ship , where it turns out that Vural had tried to make a deal with Styre in exchange for his own life . However , Styre intends to experiment on Vural anyway , this time to determine the human ribcage ' s resistance to pressure and muscular strength . He forces Erak and Krans to hold a gravity bar above Vural ' s body , making it progressively heavier until it is all they can do to keep it from crushing Vural . Styre stops the experiment temporarily to go make another report and the Doctor eavesdrops on it . The Doctor sneaks away again and meets Sarah and Harry . He tells them that Earth ' s galaxy has somehow become strategically important in the Sontarans ' never - ending war against the Rutans . Styre ' s experiments are to determine the physical limitations of humans , following which a Sontaran fleet will invade . The Doctor hatches a plan : he will distract Styre by challenging him to single combat . After a while , Styre will tire and return to his ship to recharge his energy . While the Doctor fights Styre , Harry will go to Styre ' s ship and remove a key component . The Doctor confronts Styre , lying to him that his experiments are useless : the spacemen are the humans ' " slave class " , the weakest of them all . The Doctor , on the other hand , is representative of the warrior class . Styre accepts the Doctor ' s challenge . While the two fight , Sarah and Harry free the three spacemen , then Harry climbs towards Styre ' s ship to carry out the Doctor ' s instructions . Styre nearly gains the upper hand , but Vural attacks him , saving the Doctor at the cost of his life . Styre reaches his limits and heads back to his ship . As the time travellers back away from Styre ' s ship , the Sontaran staggers out in pain , shrivelling and deflating like a balloon before exploding . The Doctor explains that the device Harry removed sabotaged the energiser , so the energy fed on Styre instead of the other way around . The Doctor makes his way to Styre ' s transmitter . He tells the Marshal that not only has Styre ' s intelligence mission failed , but that the invasion plans are in their hands . If the Sontaran fleet moves across the buffer zone , it will be destroyed . The Marshal swears revenge and terminates the signal . Erak and Krans thank the Doctor but decide to wait on Earth for the Nervans rather than transmat up to the station . As they watch , Sarah , Harry and the Doctor vanish . DVD , video and other releases . DVD releases . This story was released as " Doctor Who : The Sontaran Experiment " ( Special Value Edition ) - one of the few occasions in which a two - episode story has been released by itself . Released : Contents : Notes : Boxset release . This story was released in the " Bred for War " DVD boxset on 5 May ( Region 2 ) and 8 July ( Region 4 ) alongside all the classic series Sontaran stories . The DVD is the same as the one sold separately . VHS releases . This story was released in October 1991 as a double video , together with " Genesis of the Daleks " .