Let's Kill Hitler is the eighth episode of the sixth series of Doctor Who. It starred Matt Smith as The Eleventh Doctor, Karen Gillam as Amy Pond, Arthur Darvill as Rory Williams, Alex Kingston as River Song and Nina Toussaint-White. The show was written by Steven Moffat, and was the conclusion to "A Good Man Goes To War", although the stories are not closely connected.
Spoilers!
Three months after the events of "A Good Man Goes To War", The Doctor has been busy searching for Amy and Rory's baby, Melody Pond/River Song. Not having received any news, they summon the Doctor back to earth the best way they know how: by cutting a crop circle in a field with a car. The Doctor shows up, and then they are joined by a new character: Mels, arriving in a stolen car. It turns out that Mels, who we haven't met before, is Rory and Amy's best friend, and is being pursued by the police. She hijacks the TARDIS, saying "I've got a gun, you've got a time machine, what the hell, let's kill Hitler".
We are treated to a flashback where we learn about how Rory and Amy grew up with Mels, shepherding her through a childhood and young adulthood that was prone to all sorts of troubles. We also learn more about the history of Rory and Amy's romance, which was marked by Amy overlooking Rory throughout their teenage years, until Mels finally brought Rory's obvious affection for her to her attention. And then we are whisked to 1938 in Berlin, where a shapechanging robot full of miniaturized people called The Tesselecta is out to torture Adolf Hitler. A task that is interrupted when the TARDIS crashes through the windows of Hitler's office. During the ensuing tussle, Hitler fires wildly and hits Mels (although, as some have pointed out, it might make sense that Hitler manages to shoot the only non-white person in the room). But, in what is a surprise for our three heroes, if not for the viewer, Mels regenerates into River Song, who then promptly poisons the Doctor with a kiss. The episode is then taken up with the attempt to return The Doctor to life, and to find out the motivation for The Silence, the alien race and/or religious order that is out to kill The Doctor in the first place. Hitler is left banging in the cupboard.
Of all the episodes of Doctor Who, this is probably the one I am most ambivalent about. There are two major flaws with it: first, the revelation that Mels is actually Melody is dramatically underwhelming, because she is a character we have never met before, and she is introduced only ten minutes before she is "killed" and returns to being River Song. If she had been sprinkled into the series before this, it would actually have an impact. The second issue is that using Hitler, who has never been used in a Doctor Who episode before, could be seen as tasteless. The entire confrontation between The Doctor and Hitler is rushed through, and Hitler is almost a comedic character.
On the other hand...this episode is just great in its audacity, emotional range, and inventiveness. I can't think of another science-fiction writer besides Moffat who could sit down and think "I will write a story called 'Let's Kill Hitler', but it will really be a story about not overlooking the people who love you most. And it will have a crop circle, and some overly-polite termination robots!" Like much of Moffat's work, even if you don't like the result, it is not for a lack of ambition.
After the events of this episode, we will return to a slightly more even pace in the next few episodes, starting with Night Terrors.