Caverns of Beta Delta II was a chance to get Chrístõ off Beta Delta IV without his TARDIS, to get to know a bit more about his students, and to get Humphrey into a story again. The idea of him travelling in a big squashy bag that snores and wriggles and makes noises was irresistible. Caverns, of course, are Humphrey’s own territory, so he got to play a huge part in this story.

Abseiling and mountain climbing are not something I am particularly expert on, and I have only ever been on safe tours down places like the Blue John mines in Derbyshire. But I think I know enough of the basics to make a story about climbing and exploring cave systems.

The flatpack food was first introduced in a Ten story, Fate Of The Jdica, which had Ten and his friends on a cross country ski trip in the ice age, with all modern conveniences.

It was a story about the students, really, about their strengths and weaknesses. The fact that they are all telepathic has been established already. But, of course, they have other talents. I made the three older students, Marle, Laurence and Pieter, all competent climbers who knew what they were doing, and Chrístõ forms a close working relationship with Pieter as they progress through their caverns. The two work together well, I think. The boy, Malcolm, who found he couldn’t do the climb, redeems himself by being able to retrieve the ropes telekinetically. Carlo, who can’t swim, finds his courage in the end. All of them learn a bit about themselves.

The gulf between teacher and student is very much broken down and they all come to regard Chrístõ much more as a friend. That could be dangerous with any ordinary group of students, but since Chrístõ already shares a lot of secrets with his Chrysalids, he is probably all right.

The landslide, is, of course, ridiculously ‘convenient’. But it is in the tradition of films where people get trapped in places that were perfectly fine until then. It’s no worse than Daylight or any number of 70s TV movies about people trapped in cable cars or blacked out underground trains or buried in the aftermath of an earthquake. And the scenario with the chasm played out very nicely.

As a matter of fact, only a week after writing this, I went to see National Treasure II at the cinema, and lo and behold, that has a scene where a water channel is blocked off and the pressure builds up, and it worked exactly as I described it in this story, with spouts of water building up to a massive deluge. So I’m obviously in tune with something.