10 Most Obvious Doctor Who Plot Twists Ever
5. Kate Stewart ISN'T A Zygon
The Zygon Invasion/Inversion is a story predicated on not being able to trust your own eyes. Clara is kidnapped and duplicated by the Zygons, which is an obvious twist in itself, but that's kind of the point, so we'll let it off. And then Kate Stewart gets attacked in New Mexico and is seemingly duplicated by the Zygons herself.
Except, there was never any danger of that being the case, was there?
Firstly, we'd already seen that plot point play out in The Day of the Doctor, so what would be the point in repeating it? So while The Zygon Inversion appears to be showing us that Kate is dead and has been replaced by a Zygon, we never for a second believe it. We're basically watching her infiltrate Bonnie's extremist Zygons, right up until the moment she saves the Doctor from the Zygon trap.
While it surprises the Doctor and Osgood, it leaves viewers at home unmoved. After all, was Doctor Who really going to kill off the Brigadier's daughter and leave UNIT without its one link to the past, and its current figurehead?
It's also why we didn't believe for a second that Kate (or anyone, for that matter) had actually been dusted in Empire of Death.