After a couple of shockingly poor episodes this season, A Town Called Mercy was a return to form thanks to writer Toby Whithouse.
The Doctor, Amy and Rory show up in a frontier Western town that is under siege by a cyborg gunslinger. The cyborg is after the "alien doctor" and, for a few moments we are allowed to think that this is The Doctor, before his target is actually revealed to be the town's doctor, Kahler-Jex (Adrian Scarborough).
Jex explains that his spacecraft crashed outside of town several years ago and as the towns folk pulled him from the wreckage, he has been repaying his debt by curing sickness, giving the town electricity (about 10 years before it was invented) etc
Only, The Doctor soon discovers that Jex spacecraft isn't wrecked and that he is actually a war criminal, on the run from one of his experiments - the cyborg.
This is pure Doctor Who - a classic dilemma about what constitutes justice. Is handing Jex over to the cyborg the right thing to do, even though he has been such an asset to the town.
Mercy, the town, is symbolic of America (at that time), in that it's "all about second chances", explains Isaac (Farscape's Ben Browder), the town marshal.
However, an accident puts The Doctor in the position of power to make the final decision, when the cyborg threatens to kill everyone in Mercy if he can't have Jex.
Whithouse keeps us guessing right up to the third act as to what direction the plot will go and this intelligence - so starkly absent from the two previous episodes - is what makes A Town Called Mercy stand out.
He took a very straight forward plot, then extrapolated it in interesting directions, giving all the major players key roles that allowed them to stay true to their established characters - thus creating conflict. The simple key to superb writing. Everyone had a role to play and there was never any possibility of a person acting against type and shattering the illusion of the story - even when The Doctor was waving a six-shooter around, it felt right.
Toby Whithouse should definitely write more episodes of Doctor Who.
It certainly helped that I'm a sucker for westerns and given the fact that Farscape is one of my favourite sci-fi shows the appearance of Ben Browder didn't hurt the episode either.
It's a shame then that the name of the alien species - the Kahler - sounded so much like the Kaled, the progenitors of the daleks, as that became a niggling distraction, especially when Jex was revealed as a war criminal who turned people into living weapons. I couldn't help but think: "Is this something to do with the daleks?" Which it clearly wasn't. Or was it?
Then there was Sadie the bar maid who looked like River Song. Again, you have to wonder: didn't someone see that Joanne McQuinn, especially with that western hair-do, was a spit for Alex Kingston?
It's too early to judge whether these are some form of canny foreshadowing or simply sloppy production standards.