There is trouble in Cimarron when Jing McQueen, the drunken son of wealthy cattleman Mike McQueen, shoots a local preacher and burns down a livery stable. When the preacher recovers, he refuses to press charges, and McQueen is released from jail, leaving Marshal Crown to control an angry lynch mob.

Marshal Crown tries to prevent the Houston clan from entering the Mocane Valley before it's open for settlement. The Houston's believe they'll have little competition for prime land because of the legend of a malevolent beast thought to lurk in the valley. When the wagon train is destroyed and most of its travelers killed, Marshal Crown and his men search for the culprits not knowing if their quarry is man or beast.