Pictured above, Jon Pertwee steps out into an alien environment created by blue screen / chromakey. This won’t be the last time. The BBC called this blue screen tech – the antecedent of modern green screen – “Color Separation Overlay.” It was used for the first time in the previous serial and there will be quite a lot of CSO in Doctor Who‘s seventies.
It turns out that the aliens are not empty suits as our son predicted, but hideous blue-and-black creatures that we only glimpse very briefly. And it also turns out that General Carrington is behind all the villany. Our son claims that he’s known that the whole time, but I’m not certain I believe that claim.