This is my favourite of the Lone Pine books, and the one I always think of as the first in the series.
Okay, "Mystery at Withend" is actually the first, but that is a war time story: plucky kids investigate German spy ring. The other books are general mystery/thriller stories, and "Seven White Gates", the first of this style, sets a high standard.
It has a powerful, eerie setting, as well sketched as any in Saville's long writing career.I am sure many a youthful Lone Pine fan retained a strong mental image of the disturbing Devil's Chair atop the blasted Stiperstones mountains, long after the happy denoument to this story.
It has strong characterisations, as usual, and introduces my favourite Lone Piner, the always delightful Jenny Harman. Here we glimpse her unhappy home life, a weak father and overbearing, unlovely mother driving her to rely on herself, kind of a Shropshire Lizzy Bennett (well, sort of...)
It has a coherent, believable plot, told at a rattling pace; not always a strength of these books.
It does lack a villain, but the brooding, gloomy Old Testament figure of Uncle Micah all but fills this role.
All in all, a near perfect example of children's adventure story. This is all despite the opening of the story being a bad mis-fire. Unusually for Saville, this mistake is in setting, the first chapter is set in Petronella's boarding school, rather sub-standard Chalet School, and not a scene he repeats in the rest of the series.The Lone Pine books are about adventure in the wide world (well, the wild world of England in any case) they do not mix well with school stories. But as soon as Petronella leaves the school, and meets the Romanies on the open road, the story takes off.
A great introduction to reading for enjoyment for any imaginative pre teen, even today,dare I say.