[WARNING: The Following Review Contains SPOILERS!]

The Zygon Invasion has begun! A militant group of the shape-shifting alien race have taken over UNIT and replaced certain key figures. Among these are Clara Oswald – The Doctor’s most recent companion – whose form has been taken on by the Zygon rebel leader, “Bonnie”.

The rebels’ goal is to start a new war with Earth, after outing the 20 million Zygons currently living peacefully on Earth in human form. They seek a world of their own where they will not have to hide what they are. And if 20 million of their number have to die in the process, well – better to die in fire than live in chains!

Of course The Doctor has rather strong opinions on forcing people to die for a cause – especially ones they don’t particularly believe in. This is why The Doctor created The Osgood Box and left it in the care of twin Osgoods – one human (A UNIT Scientist and Doctor fangirl) and the Zygon who replicated her.  It is said The Osgood box has the power to end the truce between Human and Zygon… but precisely how is unknown.

It could unmask every Zygon on the planet. It could kill them. It could rob every Zygon on Earth of their shape-shifting ability. Or it could destroy all of London and whoever activated the box in the first place! With Bonnie having full access to all of Clara Oswald’s memories, the race to The Osgood Box is on! But The Doctor and the surviving Osgood may not be as bereft of allies as they believe.

The Zygon Inversion is a marked improvement over last week’s Part One, The Zygon Invasion. How much of this is due to the influence of show-runner Steven Moffatt on this week’s script and how much of it is due to writer Peter Harness finally getting on with the action after spending most of Part One telling the viewers VERY IMPORTANT THINGS about how WAR IS BAD while being INCREDIBLY SUBTLE AND NOT AT ALL FORCED is up for debate. As before, it is the skill and charisma of the cast in interpreting the material that makes this episode at all tolerable and the best example of this is Peter Capaldi’s massive speech (almost certainly Moffat’s work) about the horrors of war and why The Doctor will do anything to prevent others from suffering as he has.

Beyond that, the script for this episode is a bit of an all-round mess. It is an improvement on last week, however, in that this week the metaphors are allowed to be metaphors without the characters having to explain the parallels between The Zygon Rebels and Every Religious and Political Extremist Group Ever to the audience. One particularly effective moment involves a happily assimilated Zygon having his ability to change removed by Bonnie so that she can film a video of a Zygon “rampaging” through London and leak it on-line.

It is effective, at least, so long as one does not consider that there were much easier ways for the Rebel Zygons to spread panic than by forcibly turning the Zygons who enjoy posing as humans into the equivalent of suicide bombers. But since playing the part of Bonnie allows Jenna Coleman the first chance to do some real acting in some time, I’m willing to forgive the contrivance. What I cannot forgive, however, is what these two episodes have done to the character of Kate Stewart.

Introduced as the new scientific leader of UNIT back in The Power of Three, the past two episodes have made Kate into more of a trigger-happy hawk than her father (Former UNIT leader Brigadier Lethbridge-Stewart) ever was. The woman who once spoke proudly of her soldier father saying that “Science should lead” is reduced to pumping bullets into a Zygon and being ready to gas millions of innocents.

One had hoped for a twist that this was a Zygon playing at what they thought the leader of UNIT should act like, but it was not to be. On that note, one wonders if the Cyber-Brigadier is somewhere crying tears of motor oil that they finally found an alien menace that wasn’t immune to bullets and he isn’t around to shoot them. But I digress.

The Zygon Inversion isn’t a bad episode of Doctor Who. It is, unfortunately, tied to a bad episode which limits its ability to stand on its own. In the end, it is merely serviceable.