Dick West's uncle Jed Perdue leaves him tied to a tree in the mountains to die of exposure. With Dick's death, Perdue would inherit a valuable ranch. Range Rider rescues him, then goes for help a few miles away where he meets Professor Hornbone. The professor is assembling dinosaur skeletons he is scavenging from tar pits on Dick's ranch. Range Rider and Dick have a showdown with Perdue and two henchmen in the building housing the assembled skeletons.; While out riding, Range Rider and Dick West come across a burning wagon. Range Rider rescues a man from the wagon, but he has been shot and dies soon after telling the pair to search for "El Asesino". Range Rider and Dick trail the bandits to their hideout, then flush them out with a brush fire. The bandits blow up a boulder with dynamite and escape. Later, two bandits dressed as Range Rider and Dick rob the bank in Rio Hondo. A posse finds Range Rider and Dick and the two are arrested. Later, after showing the sheriff papers proving who he is, Range Rider sets a trap to attract the gang.