This episode, ironically (given the title), feels more like a sort of middle ground. It doesn't really further the plot so much, apart from in the shock ending (which makes me really intrigued to find out what they want in Jack).

There are, however, some really epic moments. I loved Gwen's retort to the doctor that if you're turning a blind eye to the corruption going on, you can't call yourself a 'doctor' anymore, and her other badass moment when she just totally blows up the incinerators at the Wales concentration camp. The Ester fight scene with Vera's killer was also very, very cool, and extremely well choreographed.

And how cool is it to see Ernie Hudson in the Doctor Who universe? How the hell did they manage to get a Ghostbuster to appear? He must have cost a fortune!