My son greatly enjoyed it; I'm half way through. Some of the descriptions of cave passages have the ring of true authenticity that is so often lacking in children's books (and filums) and you can almost smell the dried cave mud in the club barn.
It was intriguing to see that the author's caving experience had focussed on the (presumably brief?) period when ladders were made from wire ropes with wooden rungs, which sounds like a transition stage between hemp rope and wood and electron. "I never knew that before"
I'm surprised that the cavers are all using lights held on bare heads with elastic. I wonder if this particularly reflects the author having begun his caving career with the Royal Military Acadamy Sandhurst? I though that compressed fibre helmets had rapidly been taken up by cavers in the early post-war years - or maybe they became popular some years later?
Looking at the list of other titles by this author, 'The Underground Explrorers' and 'The Underground River' are clearly caving-based but did Conon Fraser write any other caving-based childrens' novels? My son is keen to read more caving books by this author so the hunt is on!