When a small fire starts to creep through the underbrush deep within a Montana forest valley, Porter Cassel is brought in to organize the firefighters charged with containing it. The fire moves quickly from bad to worse, rapidly scaling the forest canopy and killing one of Cassel's men. Removed from command, Cassel takes the fire investigation into his own hands, discovering that the fire was not just a random flare-up, but the work of an arsonist.