There’s always a danger that a story spread out over two weeks will ultimately fail. The excitement of the first part gives way to dull mechanics in the second as writers struggle to tie up all the loose ends. Not this time. “The Zygon Inversion” was a perfect counterpoint to its mate “The Zygon Invasion”. While the initial episode of this riveting two-parter was all action and setup, the sequel was keen introspection with trappings of wounded pride and hidden pain. “Invasion” was the extrovert’s tale while “Inversion” turned inward to examine the complex issues of people forced to live on the fringe of society. It reminded us how quickly the oppressed become the oppressors. Peter Harness skewered contemporary politics but not without a thoughtful willingness to acknowledge that all sides had a right to their discontent but needed better methods to address the problem.