To the children's shock, the box containing the map is sold to an antique collector. The same man also makes an offer to buy Kirrin Island. The children realise he has unearthed the secret map and wants the gold for himself, and so begins a race for the five to get to the gold first. Thinking the children want to spend time at the island before it is sold, Uncle Quentin and Aunt Fanny allow them to go camping there for one week.