Metebelis Revisited takes the twins on their first unsupervised adventure. Metebelis Three, of course, is familiar to all Doctor Who fans who recall the 1970s. It is the planet The Doctor went to at the beginning of the Green Death and acquired (stole) a blue crystal which he gave to Jo Grant as a wedding present. Jo and Cliff sent the crystal back to The Doctor when they were in the Amazon, as the local people were frightened of it, and that led to mysterious adventures that led The Doctor back to Metebelis and a confrontation with The Great One, the leader of the spider people, and ultimately to his regeneration.

Against that background the twins arrive, looking for the same blue crystals. And they find a dead planet that has been devastated by radiation. Something happened to the planet – granddad. But something else is happening, too, and the same curiosity that got their great-grandfather into trouble so often drives them to find out why the radiation is less at ground zero than elsewhere.

The idea of the cavern that has been imbued with the intelligence of the great one came to me as I was writing. I had an idea that something should be happening within the cave, and I wasn’t going to get involved with giant spiders again, no thanks! I didn’t like spiders BEFORE Planet of the Spiders and that didn’t help one little bit. The glass walls, of course, are what might be expected where there has been intense heat from radiation. And the idea that those walls might be able to reflect the memories of the intelligence of what happened the last time a Time Lord stood in that place was a way of telling the flashback story.

The intelligence recognising Chris as ‘The Doctor’ was another idea that came to me as I wrote it. I had always intended Chris, the strongest telepath, to take on the Intelligence, but it occurred to me that one or both of them could be recognised by their DNA. In later stories, Davie, with his genius for engineering and thirst for exploration, is the one who becomes more and more like The Doctor, but in this case it is Chris who takes on the mantle and fights the creature.

And of course he wins, but as with The Doctor when he fought the Great One, it was a victory with a price to pay. This time, not a regeneration, but still Chris arrives back on Earth in a bad state. Enter the two girls, Sukie and Vicki, both strong telepaths themselves, as the Healers. The twins have their role in the scheme of things, and so do the girls.

Meanwhile, Davie has plans for the crystals, apart from a birthday present for their mum.

http://www.rdwf.org.uk/doctors/D3/s11/05planetofthespiders.htm