The second of the Fifth Doctor, Nyssa, Tegan and Turlough trilogy. The Tardis crew are looking for evidence of the deadly Richter's syndrome and land on a Forest world where they find a weird group of hygiene obsessed colonists who live in fear of infection, and of been snatched away by mysterious robots from the woods.
It's probably bad timing that I listened to this so soon after Spaceport Fear which has some similarities of plot. The idea of survivors from an earlier expedition who have developed a strange society and culture based on convoluted memories of their origins crops up here again. And the mystery of the threatening, robotic "Takers" also seems very familiar. At the heart of the matter there are no new stories, just newer versions of old ones so it is not surprising to find some repeated themes here.
Having said that the build up of the mystery of Purity colony and the robot Takers is pretty good. The weird sound effects of the forest give the first two parts a nice creepy feel. And the cast are all very good including another appearance from Hayley Atwell who was so impressive in Blood of the Daleks.
Despite the similarities with Spaceport Fear this one made more of an impact on me, and was more enjoyable, than Cobwebs. The story did seem a stretched out in the final part once the mysteries were solved but those are the constraints of the four act structure.
4 out 5 orange glowing Android brains. Let us see if the final part of this Richter's trilogy, The Cradle of the Snake can outdo that score.