In Twelfth Doctor two-parter “The Zygon Invasion”/”The Zygon Inversion” (2015), a “ceasefire” between humans and millions of shapeshifting alien Zygons living on Earth breaks down, due to a splinter cell led by a Zygon calling herself Bonnie. The story was a co-write by Steven Moffat and Peter Harness, who recalls going into “a darkened side room” with the showrunner at a screening of Peter Capaldi’s debut episode. “He pitched it as Zygons, urban thriller, and ‘Osgood didn’t die’.”