When the Baker family arrives from Boston to Lake Fortune, in rural Maine, they are welcomed by a rickety cabin with an outhouse, a thunder and lightning storm, and a creature in the attic that masquerades as a ghost. But then true adventure begins when they discover a clue left in a Mason jar on a tiny island in the lake. Soon, they are on the path of an exciting treasure hunt, one that brings Charlie and his bossy big sister Clarrisa together...