The Lone Pine Club was formed by author Malcolm Saville, initially as a plot device in his Lone Pine series of books, but subsequently as a real club that the young, and not so young, could join.
The books, some 20 of them, are all set in parts of England1, and their plots invariably require one or more of the fictional Lone Pine Club members to be kidnapped by the 'baddies' only to be rescued by their Lone Pine pals.
The omnipresent Lone Piners in the series are David Morton and his brother and sister, Dickie and Mary. These latter two are twins, and are unusual in being described as identical; which, strictly speaking, is biologically impossible2 for a brother and sister!
The first book, Mystery at Witchend, is set during the Second World War, and the main baddie is, of course, a German spy. The last book, Home to Witchend is set some 40 years later, and yet the Lone Piners - all brought together for the finale - have aged only marginally by five years or so.
It seems that Saville decided this time-warping had begun to stretch credulity, and that, perhaps, the modern background was not as evocative as earlier times. So the series was ended; and, for many real-life Lone Piners, a little bit of magic died with it.
The central tenet of the Lone Pine philosophy is, 'Be true to each other, no matter what happens'; and the message in the stories was that friendship and decency would always triumph. It seems that the books are no longer available to today's kids, and perhaps they would seem rather outdated... but it's a shame, nonetheless.