If this was the first Biggles book that you read then you would be forgiven for thinking at all of the Biggles books were like this one and thus throwing the whole series away in disgust when you discover that they are not. This one book has everything that you would expect from a 1930's pulp science-fiction story – secret cults, ageless men, robotic centipedes, and ray guns that are designed to kill people and disable aircraft. In fact, this particular story literally reads as if the entire series were like this, when in reality (as far as I know, because this is only the fifth Biggles book that I have read, which includes three collections of short stories) they are not.
Well, I think I have given away most of the plot in that opening paragraph, but I will rehash it again just in case you did not get it. Biggles is summoned by a professor who has discovered a strange mountain in Tibet, one that glows because of the amount of radium in it (and I suspect that the radium in this story is quite different to the radium in real life). However, they have also stumbled across a strange mystery involving some people dying from unknown causes, so they decide to travel to Tibet to investigate this strange phenomena.
Fortunately, they discover a place to land the plane, and then travel over to the mountain (which also fortuitously happens to be not all that far from where they have landed the plane) to discover that it is occupied by an ancient Chinese cult (who they refer to as the Chungs, and while some people have criticised Johns for being racist and degrading in this regard, I did not actually see the Chungs as being Chinese per se, but rather being members of the strange cult).
Anyway, Biggles quickly discovers that the Chungs are hostile, so he grabs his Lewis Gun (which looks like this):
and he, Algie, and Ginger run around the secret base with their other companions, which includes a Scottish sailor who had been kidnapped by the Chungs, who, upon discovering Biggles and his cohorts, manages to escape and helps them, shooting the Chungs (because while they are expert martial artists, they discover that they have met their match when they come face to face with the Lewis Gun) and pretty much destroy the base before returning home to England (after a miraculous escape from Tibet in a way that only Biggles, ace pilot, can do).
All in all this was an okay book, but it did not maintain the standard that the other Biggles book that I read (I think it was Biggles Takes it Rough) and you can't really compare them to the short stories either. Also, from what I gather, there are probably not that many, if any, Biggles books out there than run along the same theme, despite the fact that there, I believe, are bucket loads of Biggles books around for those of us who still like to read our Biggles.