The Young Adventurers is a collection of books written by Enid Blyton . They were originally published as the Riddle Series in 1997 by Collins. The “Young Adventurers” versions were published in 2004 and are illustrated by Patricia Ludlow. The names of the six books are as follows : * The Riddle of Holiday House ISBN 1841357375 * The Riddle That Never Was ISBN 0006945740 * The Riddle of The Rajah's Ruby ISBN 0006945759 * The Riddle of The Hollow Tree ISBN 0006945767 * The Riddle of The Hidden Treasure ISBN 0006945775 * The Riddle of The Boy Next Door ISBN 0006945783