As Stuart and the rest of the Little family head off for an entire summer at their lakeside cabin, the young mouse sees this as an opportunity to take on the great outdoors and show his parents he can take care of himself. Stuart enthusiatically enrolls in the local Lake Scout program only to find that the forest is a much bigger challenge than he thought. It's only with the help of his new friend Reeko the skunk that he begins to learn the ways of the forest.

The forest however has a dark secret... a monster known only as 'The Beast'--a cruel creature who rules the woods with an iron paw... and unfortunately for Stuart's friend, the pampered Snowbell, the Beast's favourite food is cat...