Quick recap
Jerry and his sister Terri spend the summer with cousins Brad and Agatha in a small New England town. On the beach they meet Sam, Louisa, and Nat Sadler, who tell them about a 300-year-old ghost in a cave. The siblings go in and find an old man who beckons them closer. They try to trap the ghost by sealing the cave with rocks, but the plan fails. The old man, Harrison Sadler, says he's no ghost but a researcher who has hunted spirits for years. His dog barks at the three new friends and gives away the truth: they're the ghosts, dead since 1641. Harrison seals them in, sacrificing himself. Back at the cottage, the dog barks at Brad and Agatha.
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