Summer vacation is nearly over, and Liza, Bill, and Jed know it's almost time to leave their grandparents and the exciting adventures they've shared on Pirate Island.
Before they head home, the trio is itching to solve the mystery of Cougar Island. But it's private property, and according to legend, trespassers will be haunted forever by the ghosts of the Cougar family. Ghosts or no ghosts, Liza, Bill, and Jed won't be satisfied until they've done some exploring.
And when they do, they make the most amazing discovery! Are those old stories true? Could the island be haunted after all?