"The Weathermonger" is apparently the third book in a trilogy, preceded by "The Devil's Children" and "Heartsease." Having not read those books, I can't comment on this installment's place in the overall trilogy or its relationship to the other two novels. I can however, say that had the blurb not informed me of two preceding books, I doubt I would have realized. It's completely self-contained novel, so in this case, one shouldn't feel that it's strictly necessary to track down the others in order to understand the story (however, you can buy the series in this omnibus edition: The Changes: A Trilogy).
Set in a vague idea of the future (or rather, as the future may have looked from a writer publishing in 1969) the story opens with Geoffrey and Sally, two siblings left adrift on a rock in the sea by their community. Confused by a knock on the head, Geoffrey is informed by Sally that their uncle has been killed after being found working on a motorboat, and that the two of them have been left to be drowned when the tide comes in.
After "The Changes," England has regressed back into primitive times, in which any machine or piece of technology is met with fear and loathing. Those unaffected by the bizarre state of mind have escaped to France, and that's where Geoffrey and Sally manage to escape - only to be sent back by the French authorities on a mission to discover where exactly the machine phobia stems from. The majority of the story concerns Geoffrey and Sally's dangerous cross-country journey across hostile territory to its surprising source, and Dickinson keeps tension high as they come across various friends and foes on the way.
I'm not sure why Geoffrey is given amnesia at the beginning, as it makes it difficult to get to know a character who doesn't really know himself (and we're never entirely clear as to whether he regains his memories). Perhaps it had something to do with the two previous books. Perhaps it was a way to get the exposition of the situation across to the reader, as Geoffrey has to have much explained to him. Either way, Geoffrey and his sister are pleasant enough kids, but they don't really seem to come alive as characters.
Dickinson writes in smooth, clear prose and the story charges along at a very brisk pace. It is a reasonably slender volume and most readers will have it done in one sitting. The book's most memorable feature is its moral ambiguity - there are no black-or-white characters or motivations here, and Dickinson's best character "Cyril Camperdown" (not his real name!) is a perfect example of this.
Altogether, "The Weathermonger" is a quick, interesting read and the irony of the last line brought a smile to my face.