Reef of Death — Paul Zindel

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Seventeen-year-old P.C. McPhee is in Australia to help his uncle solve a mystery involving buried treasure, a beautiful Aboriginal girl, and a horrifying sea creature. P.C. quickly realizes that they're not the only ones looking for the sacred treasure. An evil geologist is also determined to get her hands on it -- at any cost. P.C., his uncle, and the girl Maruul become involved in a deadly game of cat and mouse where winner takes all -- including the lives of the losers.