Fifteen-year-old Pete Jenkins and his three summer friends visit the
nearby Round Island Lighthouse after crossing the turbulent water of
Lake Huron in their tiny dingy. After exploring the island they return
to find their picnic basket turned upside down and a warning message in
their boat.
The threat on their lives only heightens their curiosity and leads them
on the trail of dangerous thieves.
Along the way the four friends discover a side of Mackinac Island that
goes beyond fudge and horses---and eventually leads them into
life-threatening danger.