When a good friend of the boys strikes gold on his property, he gets the Three Mesquiteers - Stony (John Wayne), Tucson (Ray Corrigan) and Lullaby (Max Terhune) - to help keep an eye on things. The greedy Mayor of the town soon finds out about the gold and tries everything to get he’s hands on the mine. When their friend turns up murdered, the Mayor pins it on one of the Mesquiteers, Stony. Now the boys must try and solve the case before the town folks kill Stony and the guilty get away with everything.