A famous lawman named Pinkerton (Don Galloway) comes into the mountains looking for Adams (Dan Haggerty), intent on returning him to town for trial. Mad Jack (Denver Pyle) runs into Pinkerton and quickly heads off to warn Adams.
In the meantime, a mountainous volcano has become active, threatening to erupt and destroy an entire valley. Nakoma (Don Shanks) rushes to Adams' cabin and tells him of the impending danger. Adams, Ben and Nakoma set off the Thunder Mountain, hoping to rescue what animals they can before the volcano erupts. Mad Jack tries to stop them, proclaiming that the lawman lurking about is an even greater danger to Adams.
Pinkerton intercepts them as they head for Thunder Mountain, but Adams is determined to save the animals. He makes a deal with Pinkerton, agreeing to give himself up and return to town for trial, if the lawman will allow him to rescue the animals from the volcano first.
They all make their way to the volcano, encountering landslides and earthquakes on the way. Adams charges into the smoke and heat to rescue animals, and is soon followed by Nakoma, Jack, and even the amazed Pinkerton. When it's all over, Pinkerton decides that a man of Adams' character couldn't be guilty of any crime. He tells them he will return to town and report that he couldn't find any man named Adams in the mountains.