The four Gareth children have always led a very quiet life in London with their parents - until Dad suddenly gets ill abroad, and Mum has to go out to look after him.

The Gareth children are shipped off to Great Aunt Dymphna, who lives wild in an extraordinary half-ruin in Ireland. Here they are not only expected to look after themselves, they also discover that they have company - a mysterious boy who announces that he is on the run. The children hide him from his pursuers - but who are they? And who is the boy? The children are determined to find out...