So in Series 2 they tried a "non doctor centric" episode. While this idea was intriguing and gave a different dynamic to the series, the writing, in particular the disappointing "absorbaloff", wasn't quite up to scratch (don't get me wrong it was still a great episode!). However, this time round, they appear to have honed their skills and come up with one of the best episodes yet, certainly one of the highlights of this series.
The format of this episode gave us a break from prosthetics, animal heads and spaceships and produced a extremely clever and frightening episode. It was superbly acted by Carey Mulligan (Sparrow) and if she were to return in future it would be great, she fit into the Doctors universe with perfect ease. I look forward to other "non doctor centric" episodes in the future. I also look forward to more episodes written by Steven Moffat, easily one of the best writers the show has.