In the third book in this quartet, Franny and her father Gerard are camping in the Stone Circle near Herpeton. Stone Pond has dried up for the summer and Franny finds a dragon stone at the bottom. She moves the stone and finds the entrance to a tunnel which leads her to a tower and another world.
Used availability for Toby Forward's Wyvern Summer
July 1994 : UK Hardback
August 1995 : UK Paperback