Summer vacation has arrived for the children of the Morgan family of Morning View, Kentucky. Clever young Scout Morgan makes an amazing discovery: a secret room in their house, where they discover their long-lost Grandfather Gunn's steamboat chest containing a variety of treasures and mementos. The most tantalizing item they find is a detailed map purporting to show the hiding place deep in a cave of another chest, this one full of gold coins! Grandmother Gunn believes the cave is located upstream along the Looking Glass River that flows past their town. Scout and older brothers Clay, Cliff and Stone set off in canoes on a quest to find the treasure. When they reach the area along the Looking Glass where Scout thinks the cave is, they are startled to find they have sailed straight into Seckatary Hawkins and the boys of the Fair and Square Club!