An only child, together with her two long-time friends, another ten-year old girl and her twelve-year old brother, defy their parents and set off on an exploration that traps them in a dangerous place and throws them upon the hospitality of two strangers and their own wits and perseverance to return safely. Death is always near and claims a fairly predictable victim in the end.
Ten year old Lilly Ariadne's family and Iason and Lydia Diamondes' family have been vacationing on the island of Thalassos for many summers. This summer is no exception. Lilly's American teacher-for-a-year, Petra, joins them. On a tiny island off the main island, where the children and generations before them have always played, the three children accidentally discover a new and dangerous place: a tunnel. As they explore the tunnel, they are suddenly prevented from getting back home by the closing of a giant stone door. They must continue down the tunnel and come out in a wild area where strange soldiers capture 12-year old Iason and keep him overnight. The two 10-year old girls must avoid capture, find food, and figure out a way to get back. The search for the children is complicated by a partial cave-in of the tunnel, and one parent is injured. The children and the teacher rescue the parent and come out safe, mostly