Planet of the Spiders

Once upon a time the Doctor visited Metebelis 3 and took a large, perfect blue crystal. He gave it to Jo Grant as a wedding present when she and Dr Clifford Jones left for the Amazon. But now she has posted it back to him, claiming that it is frightening their native guides. Meanwhile the disgraced UNIT officer Mike Yates has joined a Buddhist retreat, where he has grown suspicious that some of his fellow students are in contact with some kind of alien power. Earth is in danger from a powerfu...