The Zygon Inversion for about the 3/4 of it’s story comes across as a perfectly respectable continuation of events from The Zygon Invasion (mind you–if one doesn’t look too closely at the plot holes).
And then it happened.
One of the basics tenets of Doctor Who here at THT Worldwide is that despite the overall longevity of the program, there are precious few ‘magic moments’ which forever define a particular era or actor within the program. We’re especially fond of ‘Binro the Heretic’ from The Ribos Operation or the Davros/Doctor exchanges from Genesis of the Daleks. The end of episode 3 from The Caves of Androzani ranks right up there. Every fan carries their own mental list of what’s important to them.
The Capaldi monologue near the end of The Zygon Inversion makes it’s arrival onto this list, and that alone elevates it and marks it as a special story. We’re still not sure about this being the best two-parter of the Series to date, but it is easily the best moment.