I think there was a meeting post A good man goes to war during the break, and the aim was to come up with a totally provocative title to try and get the viewers back for more (viewing figures had been strong.)
Amy and Rory's friend Mel hijacks the TARDIS and forces the Doctor to travel back to Nazi Germany to kill Hitler. Mel's later regenerates into River Song, after being accidentally shot by Hitler, who himself is trying to shoot an alien machine, The Teselecta, who is disguised as a German officer. The Teselecta are a group of miniaturised people who act as a justice agency and wipe out people with crimes against humanity. We learn River's crime, and why she has been imprisoned.
Where to start, I actually really loathe this episode for many reasons. The characterisation of one of the most evil men in world history I found a little distasteful, especially for some of the younger viewers. Am now pretty much disliking Amy, she's become a rather dislikeable sidekick. The flashback of Donna made my heart sink, why couldn't we have had a companion with a personality!! I was not impressed with the Teselecta, didn't feel right somehow.
The best thing about this episode is Alex Kingston, she plays River with a huge burst of energy and fun, she is brilliant. I find River's change of heart a little questionable, all of Madam K's training undone by the TARDIS.
I love how my very own Swansea doubles for lots of Berlin, oh if only!!
Nearly a disaster 3/10 Putting Hitler in a cupboard puuurleeease!!