Sam, Otter, Atim, and Chickadee are four inseparable cousins growing up on the Windy Lake First Nation. Nicknamed the Mighty Muskrats for their habit of laughing, fighting, and exploring together, the cousins find that each new adventure adds to their reputation. When a visiting archaeologist goes missing, the cousins decide to solve the mystery of his disappearance. In the midst of community conflict, family concerns, and environmental protests, the four get busy following every lead. From their base of operations in a fort made out of an old school bus, the Mighty Muskrats won't let anything stop them from solving their case!