A Town Called Mercy ( TV story ) From a production standpoint , this story was notable for being the first episode of BBC Wales whose visual effects were not credited to The Mill . Instead , the credit was given to Space Digital . The episode reintroduced how war created consequences , particularly what happens to the survivors and those seeking revenge . It is also the first time that the Doctor considered forgoing mercy towards a guilty man , and allowing the pursuer to enact their revenge . As the Doctor would put it , every time he was kind and allowed his enemies mercy , they would continue slaughtering innocent lives . Synopsis . Missing Mexico by 200 miles , the Eleventh Doctor ends up in Mercy , Nevada , where something ' s not quite right . . . The locals are hostile to strangers , and a border of stone and wood surrounds the town . As the Doctor soon finds out , a gunslinger is behind this , and not just an ordinary one . Plot . Against the backdrop of a starry night desert , an unseen woman with a American western accent narrates a story her great grandmother told her when she was a girl . . . a story about a man who fell from the stars and was weighed down by the things he had seen , giving the impression it might be yet another legend about the Last of the Time Lords . A cyborg known as the Gunslinger shoots down a probe in the middle of the desert while chasing Kahler - Mas . The cyborg tells his victim to make peace with his gods , to which Mas retorts that they are his as well . The Gunslinger says they are not his gods any more . Mas tries to pick up a piece of debris to defend himself , however the cyborg knocks it away and prevents his target from moving . Pinned to the ground by the Gunslinger , Mas is resigned to his fate and asks his executioner if he ' s the last of the people he ' s hunting down . Before opening fire , the Gunslinger replies that there is just one more : " the Doctor " . In the desert during the daytime , the Doctor , Amy and Rory examine the population number on the sign of a town called Mercy , seeing it has 81 inhabitants . There are several odd things about the town including a sign saying " KEEP OUT " and a strange stone and wood boundary line surrounding the town . According to a scan with the sonic screwdriver , it is just what it looks like , nothing else . The trio enter the town , unaware the Gunslinger is watching them . Walking down the street , the trio notices no - one is outside ; instead , the townsfolk are inside , giving them hostile stares . Even more odd , however , is that the town is using electricity , which will not be discovered until about ten years later . Rory is not that concerned , as it ' s only a few years off ; the Doctor jokes back at him that he said the same thing when he left his mobile phone charger behind in Henry VIII ' s en suite . Because of all the odd events happening at once , the Doctor wonders if someone has been peeking at his Christmas list . They enter the saloon , where the Doctor orders a drink ( " Tea , but the strong stuff ; leave the bag in . " ) They ' re asked by the patrons who they are . As the Doctor introduces himself , Amy and Rory , everyone stands up ; the Doctor is impressed with how polite they . He then notices someone measuring him , stating he doesn ' t need a new suit ; the man tells him he ' s the undertaker , not a tailor . One of the patrons asks if the Doctor is an alien . Surprised , the Doctor says that in " his " terms , they ' re the aliens , but in " their " terms , he is indeed an alien . The patrons get up from their seats and grab the three of them , dragging them to the edge of town . They toss the Doctor outside the boundary and hold him at gunpoint to prevent him from coming back in ; they hold Amy and Rory still to prevent them from helping the Doctor . A man spots the Gunslinger approaching and they prepare for the worst as the preacher says a prayer . At the last second , however , a shot is fired from the crowd . The town Marshal , Isaac , appears and tells the people to let the Doctor and his friends back in , pointing out the Doctor is not the one the Gunslinger wants . This is met with defiance from the crowd as the Doctor fits the description of who the Gunslinger demanded — an alien doctor . However , Isaac tells them that they " know " who the Gunslinger " really " wants , saying it ' s no reason to send the Doctor to his death . Isaac orders the Doctor to quickly get back inside the boundary . He does , and the Gunslinger departs , appearing angry . Back in his office , Isaac explains to the travellers that the Gunslinger appeared three weeks ago , placing the boundary around the town and demanding they hand over the " Doctor " . Though he hasn ' t killed anyone , he ' s stopped supplies and reinforcements entering , and the town is slowly starving to death . When someone tried exiting the boundary , the Gunslinger shot at him , putting a hole through his Stetson . The Doctor believes the Gunslinger had poor aim , but Isaac point out that the hat was the target . This annoys the Doctor , who loves hats . Amy reminds the Doctor they were supposed to go to Mexico ' s Day of the Dead festival . The Doctor ignores her complaint , demanding the Gunslinger ' s real target ; he knows that the Marshal ' s office would be the safest place to keep him if the townsfolk want to hand him over . Though Isaac protests , a voice tells him to stop putting on the act ; it comes from the cell . A man pulls the blanket hiding him off and introduces himself as Kahler - Jex . The Doctor is delighted to meet Jex explaining the Kahler are a race renowned for their technological expertise . Jex tells them that his ship crashed out in the desert some years ago . He was rescued by the townsfolk , who took him in . Since then , he became the town doctor . He cured an outbreak of cholera and used the remains of his ship to give the town electricity . The Doctor is curious why the Gunslinger is after him . Isaac interjects to defend Jex , saying Mercy is a town of second chances . He is also angry that the townsfolk are thinking of turning their friend over to the stranger . The Doctor decides to use the TARDIS to help Jex escape and evacuate the town , but first they must engage in a little slight of hand to get past the Gunslinger . Grabbing the Stetson Isaac showed him , the Doctor borrows the Preacher ' s horse . The Preacher has named the horse Joshua , but the Doctor tells them that the horse prefers the name Susan . He rides out to collect the TARDIS . In the meantime , Isaac , dressed in Jex ' s hat and coat , runs off along with Rory in another direction to buy time . The Gunslinger takes the bait and chases after the two men , but curiously holds back on firing when his systems warn of the high risk of hitting Rory . In town , Amy comforts Jex , who tells her that he knows she ' s a mother . Curious , Amy asks how he knows . Jex says it ' s because it ' s in her eyes : kindness , sorrow , and love . He goes on to say that he ' s something of a father himself . In the desert , the Doctor finds the power cables from Jex ' s ship , with the horse protesting that he should stay on task . However , the Doctor is not one to give up on a mystery ; he starts following the cords back to the source . Jex notices power fluctuations in the town , from the Doctor messing with the cords . Jex becomes worried that the Doctor isn ' t following their plan . Amy simply says , " Welcome to my world . " The Gunslinger catches up to Rory and Isaac and pins them down behind a cliff face , having switched to heat - seeking vision to find them more easily . The Doctor finds the Kahler ship hidden , but not damaged as Jex had claimed . After some effort , he manages to open it but trips the ship ' s alarm : alerting Jex and the Gunslinger , who breaks off his pursuit of the other two men . In town , Jex is panicking because the Doctor has gone against the plan . The Doctor enters the ship and manages to override the defense system . He asks the computer what it knows about the Gunslinger . Unfortunately , the ship does not understand the term , so the Doctor tries a different approach and asks it about its crew . His request brings up logs detailing horrific experiments . The Doctor watches in silent shock , listening to Jex calmly detail the events as his victims scream in the background . Back in Mercy , Amy finds herself staring down the barrel of a gun held by Jex . He assumes that the Doctor has learned some things about his past which the townsfolk won ' t understand or forgive . He is going to flee and take Amy with him as a hostage , since the Gunslinger ' s programming forbids him from harming civilians unless the situation is extreme . Jex ' s escape is thwarted by the return of Rory and Isaac , who demand answers . In the desert , the Doctor leaves the ship and comes face to face with the Gunslinger , poised to attack . He manages to get the alien to stand down by revealing he knows what Jex did and he knows who the Gunslinger is . The cyborg lowers his weapon slightly . The Doctor has worked out that the Gunslinger is one of Jex ' s " test subjects " . He pleads with him to spare the town and let Jex be brought to trial . The enraged cyborg refuses , but reveals that he hasn ' t gone after Jex in the town because he doesn ' t want to harm the civilians who would likely get in the way . He leaves , but warns the Doctor the next person who tries to leave the town will be killed unless the Kahler is handed over . At the Marshal ' s office , Jex tries to wave off his actions as a moment of panic . The Doctor returns and accuses Jex of being a liar and murderer . He explains to Isaac , Amy and Rory that the Gunslinger is a cyborg created by Jex and a team of scientists . He goes on to explain that they took unsuspecting volunteers on the pretext of military training and experimented on them . Those that did not die were turned into weapons . Rather than deny his actions , Jex admits and even defends them , explaining Kahler suffered a devastating nine - year war which decimated half the planet . Kahler authority ordered their scientists to create weapons able to end the war ; they did . In a week , the cyborg army defeated the enemy before deactivating . Unfortunately , the Gunslinger didn ' t deactivate . Jex guesses he was damaged in battle , restoring his original personality and allowing him to disregarded pre - programmed orders . Since then , he has hunted down and killed those responsible for turning him into a monster . Jex is the last one remaining . The group is unsure of what to do . Rory believes that they should hand Jex over to the Gunslinger : he is a war criminal who deserves to pay for what he ' s done , and there is no reason why everyone in town should die for him . However , Amy and Isaac disagree with him . Isaac points out that Jex saved the town from cholera , while Amy doesn ' t believe it ' s their place to march a man to his execution . The Doctor struggles with the decision . Jex observes this , and says that the Doctor could never make a hard choice like he had . This provokes the Doctor ' s fury , as he drags Jex to his feet and marches him outside . Rory attempts to stop Amy from interfering , pointing out that it is Jex or them , but Amy isn ' t willing to let the Doctor do what he ' s about to do . The townspeople gather as the Doctor pushes Jex over the boundary to face his surviving victim ; he even points a gun at him , not knowing if he would use it or not . Amy stops the Doctor by also grabbing a gun , pointing out that this is not his way . The Doctor responds that every time he faces evil he tries to understand , and has even shown mercy to his enemies , such as the Master and the Dalek s ; however , each time , they ' ve come back and killed again . For once , he is going to think of the victims , and let Jex ' s victim get revenge . Disgusted , Amy tells the Doctor that this is what he becomes without any companions to hold back his dark side ; she reminds him how they normally resolve these problems . The Doctor is persuaded , deciding that he cannot allow this ; Jex needs to be persecuted , not killed in the Gunslinger ' s vengeful rampage . Before the Doctor can get Jex back over the boundary , the Gunslinger appears behind him ready to kill . The scientist addresses the cyborg by its original name Kahler - Tek ; having remembered the names of all the test subjects . He pleads with Tek that he has changed , but the cyborg doesn ' t relent and opens fire . Isaac , however , steps in the path of the blast to save his friend . He is gravely wounded . With his last breath , he makes the Doctor the new Marshal and tells him to protect the town . A distraught Doctor sends Jex back to his cell ( ordering the townsfolk to keep him safe ) . He confronts Tek , saying this must end . The cyborg agrees and offers a final ultimatum ; hand over Jex by noon tomorrow or everyone will be killed . As the Gunslinger departs , a shocked Amy exclaims that the Doctor is now the Marshal of the town ; he retorts " and you ' re the deputy . " Night comes , and the Doctor wonders what he should do , as the undertaker gives him a cup of coffee . If Isaac thought the Doctor was good enough to be Marshal , the undertaker has complete faith in him . However , he begins taking measurements again before the Doctor sends him away . The preacher comes into the Marshal ' s office and greets the Doctor , along with Amy and Rory . He tells them to come outside as there is a lynch mob arriving . On the preacher ' s suggestion , the Doctor grabs the gun and holster , putting them on . They go outside to greet the mob . They tell the Doctor that he should go for a walk ; when he returns , Jex will be gone and he won ' t need to feel guilty . However , the Doctor tells them that it would betray the town ' s principles and Isaac ' s sacrifice . They again explain that they are only concerned for their families ; a boy aims a gun at the Doctor . The Doctor asks him if he really has the courage to pull the trigger , eventually talking him and the mob down . Once the mob leaves , the Doctor returns to the cells to talk with Jex , who also tries to goad him into handing him over to Tek . The Doctor tells him that he won ' t . Sensing how conflicted the Doctor is , Jex says it would be so much easier if he was just one thing , instead of two ; the mad scientist or the benevolent doctor . Finding Jex ' s attempt to goad him amusing , the Doctor says it ' s a pretty clever idea on how to make up for all the lives that he took , being the town ' s doctor . However , it ' s not up to Jex to decide when his debt to society is paid . Jex then explains that he fears dying . Kahler religion says that once he dies , he must climb a mountain , carrying the souls of all those whom he wronged in life ; Jex cries that Isaac , his only friend in Mercy , will be added to his load . The Doctor slightly sympathizes . Come noon the next day , the Doctor faces off with the Gunslinger in a duel instead of handing Jex over . Facing the cyborg with his sonic screwdriver , he uses it to produce a high - pitched frequency that shatters glass and disorients the Gunslinger . The Doctor takes advantage of his confusion and runs off , as the Gunslinger fires random shots . The townspeople , who had used make - up to copy Jex ' s facial marks that the Gunslinger uses to ID him , run about to cause confusion . As part of the Doctor ' s plan , Jex uses the confusion to escape town and head for his ship . Back in town , the Gunslinger searches for Jex , breaking into the church and frightening the patrons . Catching sight of a scared little girl , the Gunslinger lowers his weapon and leaves . Tired of his automatic targeting falling for the Doctor ' s trick , the Gunslinger switches to manual , finding the Doctor hiding near by . The Doctor tells him that Jex has gone , enraging the Gunslinger . Jex calls from his ship explaining that if he fled to another planet , the Gunslinger would follow him and put others in danger once more . Jex tries to make peace with Tek , asking him about his home town and how sorry he is for the terrible things he did . Jex then activates his ship ' s self - destruct and kills himself , something the Gunslinger sees as honourable . Because the Gunslinger sees himself as nothing more than a weapon of war , he prepares to self - destruct a safe distance in the desert . However , the Doctor tells him that while he may have built as a weapon of war , he can now protect the peace instead . Later , the Doctor has brought the TARDIS to Mercy to collect the electronics Jex left behind , not wanting to damage history . He asks Amy and Rory if they ' d like to find out what happened to the monkeys and dogs that were sent into space during the 50s and 60s ; apparently , they won ' t believe where the animals all ended up , which the Doctor finds amusing . However , Amy and Rory tell him it ' s time they went back home as their friends might start to notice that they age faster ( due to the time they spend away with the Doctor ) . He complies and they board the TARDIS . The Doctor tests to see if he can draw faster than someone before entering himself . The woman narrates again , saying Mercy was already used to the strange and unexplainable her great grandmother was a little girl at the time . The little girl from the church is seen walking off a short distance from the town , as the woman explains that Mercy has never had any kind of official law enforcer since then , but the residents never seem to worry , as if they have a secret protector . The little girl looks off at a hill , where the Gunslinger is standing . Gazing into the distance , a close up of the Gunslinger shows that the Doctor has made him the new Marshal . Kahler - Tek smiles and begins his watch over the town of Mercy . Home video releases . This episode , along with the rest of the first half of the series was released on DVD and Blu Ray on the 28 October 2012 .