English background (possibly coast of Cornwall?) for an exciting mystery adventure, as 14-year old Philip Mannering takes two youngsters, Jack and Lucy-Ann Trent to Craggy-Tops, where he and his sister stay during the holidays. There -- half way up a steep cliff above the sea -- the four children are precipitated into adventures involving hidden tunnels, a ghost ridden island, buried copper mines, counterfeiting, strange lights at night, and mysterious doings by the servant, Jo-Jo. Jack's parrot, Kiki, lends a bit of spice and humor.