Davis Ross creates a group of vigilantes to drive out a casino owner who has a bad influence on the town. When a couple of members of the group realize that they could have the same influence on the innocent members of the town and clean up financially, they create the Purple Vigilantes headed by the mysterious Number One. When these vigilantes murder during their plundering, Ross is accused of being the head of this group while being completely innocent. Stony, Tucson, and Lullaby try to get Ross safely out of town, under the sheriff's watch, see their plan fail when the sheriff is killed and Ross is framed for the murder. The Three Mesquiteers try to find the secret to the Purple Vigilantes and discover it's leader who could be banker McAllister, lawyer Drake, or Jones, a mysterious stranger. Our heroes try many methods before trying to bait a trap with a record of their crimes. The first 40 minutes of the film shape up to be perhaps the best of the entire series with brilliantly filled action sequences, gunfights, and use of the caves as the HQ of the Vigilantes, but the climax of the film is really weak as a setup to the mystery villain's identity revelation as well as the final conflict against the Vigilantes. Fine film to watch, but could have been better. Rating, 6.