One of the reasons Doctor Who has endured for so long is its ability to incorporate pretty much any genre you might fancy. You've got a character who can literally pop up in any time period, anywhere in the universe, and you don't even need to waste any time explaining why. It's just what he does.
That's certainly how this story gets started, simply opening with the Doctor, Rory and Amy in Texas in 1861, at the outskirts of Mercy, a town with 81 residents, a mysterious barrier of wood and stone and a big ol' Keep Out sign. That's more invitation than warning to the Doctor, of course, and barely five minutes into the episode we've established that the town is under siege from the Gunslinger, a sort of Terminator/RoboCop hybrid who is demanding the townsfolk hand over the “alien doctor” for execution. For once, it's not our Doctor he's after.
There's another alien in town – Kahler-Jex, a refugee from a distant extra-terrestrial war who has brought a cure for cholera and rudimentary heat and light to the people of Mercy, who seem to overlook his bizarre facial tattoo by way of a thank you.
There's got to be a twist in the tale though, and the script wisely gets it out of the way early. Jex is not as innocent as he seems, nor is the Gunslinger the remorseless monster he appears to be. In actual fact he's a weapon, one of an entire army of cyborgs created by Jex and his comrades in order to end the war. Many died on the operating table, and the episode quickly veers from broad western pastiche to something more in keeping with Who's chewier moral depths. The quandary at the heart of the episode is summed up in the title – who deserves mercy, and who gets to decide when it should be handed out?
There are a few heavy handed moments along the way. We could have done without Jex giving the Doctor a stock “we're a lot alike, you and I” speech, and following last week's jarring scene of the staunchly pacifist Doctor dooming a villain without blinking, we once again find him leaning towards ruthless pragmatism and harsh punishment. It's fine if that's to be the theme of this season, but it still feels a little like it's come out of nowhere. Amy remarks that “this is what happens when you travel alone for too long” during the Doctor's most bloodthirsty moment, but that doesn't really explain where this hard and brutal streak has come from. The Doctor wrestles his conscience into shape by the end, however, and the payoff for both Jex and the Gunslinger is satisfying, if a little obvious.
Unless I'm mistaken, this episode also marks the first time the show has dipped into the wild west, and thankfully it's handled with restraint. The town itself has a fairly obvious backlot feel, which is rather charming, but the cliches are dispensed with briskly and with no small amount of wit. To begin with, it felt a lot like Back to the Future III, as it ticked off the western movie tropes – not least the obligatory saloon entrance which causes everyone to fall silent and the piano player to stop playing – but it's almost as if the show is rushing through these moments out of obligation, with a wink and a nod. By the time it's recreating High Noon, it feels like a fairly organic part of the larger story rather than just an iconic image that needed to be recreated. And, let's face it, the image of Doctor Who in a stetson, facing a cyborg in a quick draw duel, is the sort of thing that's hard to begrudge, even if it reeks a little of DeviantArt fan fiction.
Speaking of which, I'd love to know how Jex got his hands on Mork's spaceship.
This was a very Doctor-centric episode though, with Rory and Amy very much pushed to the sidelines. Amy got a couple of good lines, but I don't think Rory had more than five lines in the whole thing. Judging from the teaser for next week's episode – "The Power of Three" – that's surely deliberate, as it seems Amy and Rory are growing tired of being dragged around the universe by their bipolar alien friend. Companions usually get killed off or left behind by the Doctor – it'd be very interesting to have the Doctor be the one who gets dumped for once.
So, all in all, an enjoyably offbeat episode, that doesn't use its setting as a crutch for too many obvious beats, and instead advances the characters in intriguing ways. The main criticisms would be that some of those “American” accents were terrible, and the Gunslinger's mush-mouthed voice was more than a little silly. One of the benefits of Doctor Who, of course, is that a little bit of silly often makes it all the more fun.
It seems that fun is going to be in short supply in the coming episodes though, as we count down to the Ponds' exit. It does feel like the show is trying to wean us off them, just as the Doctor and Amy are slowly circling away from each other, no doubt aware of just how popular those characters – particularly Amy – have become. I'd hate to see them become over-exposed or under-used, but it's still going to be a wrench when they go. And if the ruthless Doctor we've seen the past few weeks is what he's like when he's been alone for a little while, what will he be like when he's left behind completely?