The TARDIS brings the Doctor, Amy and Rory to the old west, where they find an entire town that seems to have walled itself in. The locals are more suspicious of the three strangers than the time travelers expect; they’re warned that stepping outside the barrier at the edge of Mercy leaves one open to the mysterious Gunslinger. Only the sheriff, Isaac, prevents the townsfolk from throwing the Doctor across the barrier and leaving him to his fate. The Doctor learns that the Gunslinger wants the locals to hand over a stranded Kahler named Jex, who has helped the people of Mercy install electricity decades ahead of time, powered by his crashed ship. But Jex doesn’t dare stray outside of Mercy, and a visit to his ship shows the Doctor why: Jex was a military surgeon performing augmentations on Kahler soldiers, and the Gunslinger was among his patients – and is one of the few who lived. The saviour of Mercy is a war criminal, and the Doctor feels an obligation to see that justice is done. Isaac dies protecting Kahler Jex from the Gunslinger’s next attack, and leaves the Doctor with the sheriff’s badge, a tough decision to make, and a slowly growing lynch mob to face.
written by Toby Whithouse
directed by Saul Metzstein
music by Murray GoldCast: Matt Smith (The Doctor), Karen Gillan (Amy Pond), Arthur Darvill (Rory Williams), Andrew Brooke (The Gunslinger), Adrian Scarborough (Kahler-Jex), Dominic Kemp (Kahler-Mab), Joanne McQuinn (Sadie), Byrd Wilkins (The Preacher), Garrick
Hagon (Abraham), Ben Browder (Isaac), Sean Benedict (Dockery), Rob Cavazos (Walter)
Notes: American actor Ben Browder is best known for his starring role in another popular science fiction series, Farscape, and for taking on the thankless job of succeeding Richard Dean Anderson as the star of Stargate SG-1 in its final two seasons. Garrick Hagon has previously appeared in classic Doctor Who (1972’s The Mutants), a few years before being cast as Biggs Darklighter in Star Wars, and more recently in the Big Finish audio Doctor Who story Axis Of Insanity.
LogBook entry & review by Earl Green
Review: Science fiction loves to tackle – usually from an oblique angle so you can’t spot the real story – the topic of Josef Mengele, who claimed to be on a quest for medical knowledge but made his patients (all of them Jewish children interred in Nazi concentration camps) pay a grotesque price for being his chosen guinea pigs. (In fact, the name of the alien race in this story, Kahler, is a reference to a medical colleague of Mengele’s.) Just about every SF series under any particular sun you can think of has treated that historical event, from Babylon 5 (Deathwalker) to Voyager (Nothing Human) to others I’ve probably 
forgotten, so it was Doctor Who’s turn. Fortunately, this topic gets a slightly better thought-out, more considered interpretation than, say, capital punishment got in Boom Town.
Dropping Ben Browder into a Doctor Who episode – in a obvious-and-yet-less-than-obvious role, no less – is an inspired move from both the casting and publicity angles. He gives Isaac a very un-Crichton-like world-weariness, far from the usual action hero fare he stars in, but perhaps the biggest surprise is that he’s not in that much of the episode, getting killed off far earlier than one might expect for the episode’s “name” guest star.
The Doctor’s deliberations on the nature of justice ring far more true than in Boom Town (where he was helpfully saved from having to render a judgement by virtue of things starting to blow up – handy, that). Here, he must make a decision, convince everyone (including, in this instance, his own companions) of its merits, and see it through regardless of the inherent danger. There’s a lynch 
mob whose anger he must cool. In all, from a morality play standpoint, it’s possibly the most interesting Doctor Who episode since Midnight.
The Doctor comes dangerously close to having to be Kahler Jex’s executioner and not just his judge, but fate – and Jex’s own remorse – manages to intervene, and though it’s not an unsatisfying conclusion, I can’t help but wonder what would’ve happened if the decision had still rested firmly with the Time Lord. Still, compared to some of those other treatments of this basic storyline, it’s impressive how far things get before the Doctor is absolved of the responsibility to see justice done. A Town Called Mercy is a surprisingly engrossing episode.