When her parents send her to stay with a grandmother she hardly knows for the summer, Elen is furious. Gran lives on a tiny island and doesn't want her either - it's not an easy start. Gran's idea of childcare is to give Elen a map and tell her to explore. After saving Gran in a storm, Elen finds a picture that she's sure is a clue to hidden treasure. She investigates and finds a very different treasure from the one she expected.