Much as Peter and Anne Mason loved Cape Cod and the old house that had belonged to their grandfather, they had to face the fact that their father didn't like it at all. Determined to enjoy what may be their last summer on the Cape, Peter and Anne work hard to buy a small boat from old Captain Amon. Perhaps they could even interest their father in fishing. But before they save enough money for the boat, Peter discovers a theif hiding out on the island.