The Windy Lake First Nation's lands have been shared with cottagers for fifty years, but no one can agree on where the reserve land ends. The only thing that can prove the boundary is a steel surveyor's pin with the borders of the Windy Lake reserve etched into its head.

When the Mighty Muskrats hear that the pin was stolen years ago—and that it is connected to their grandpa's mysterious past—they make it their mission to find the missing pin and prove that the land belongs to their people. But the mystery gets tense when Grandpa becomes a suspect. Cousins Sam, Otter, Atim, and Chickadee must find that pilfered pin!