William Corlett 
Tunnel Behind The Waterfall [EPUB ebook] 

It is summer and the long holidays at Golden House stretch before William, Mary and Alice Constant. Hot lazy days of swimming and picnics . . . until a new and terrible shadow steals over the valley and the children are plunged into a desperate adventure to save it from greedy developers. Once more they are pulled into the Magician’s world and his eternal battle between good and evil. But without the Magician’s trust and with evil Morden’s powers now stronger than ever, they have a huge task on their hands.