“The Zygon Invasion” gives us a classic Doctor Who incursion, generated from the Doctor’s attempt to resettle 20 million Zygons on Earth. What could possibly go wrong with such a plan? The Doctor (Peter Capaldi) and Clara Oswald (Jenna Coleman) once again join forces with Kate Lethbridge-Stewart (Jemma Redgrave) and UNIT. The return of a classic Doctor Who creature enhances the story, and the Zygons are formidable opponents.