Skeet's grandfather, Overdare, was an old deer mouse with no liking for beaver. 'Beaver,' he told Skeet, 'think they know the way everything ought to be in any place they settle down. If it isn't that way, they make is so, and they don't care a bit what happens to anyone else in the process.'
When a colony of beavers settles in Skeet's peaceful valley and begins constructing a series of dams, the lives of all the wild creatures who have made their homes there are threatened. Skeet and his family escape the danger but what happens to others not so lucky is soon apparent. Meanwhile, the beaver work on, oblivious to the effect of their labors on the environment of the valley.