Ken Williams pursues a masked, mysterious villain known as "The Rattler," who terrorizes those involved in the building of a tunnel.
Ken Williams and Corwin Transportation Company are attacked by a mysterious man known as "The Rattler." Ken pursues The Rattler's men on his horse, Tarzan.
After a coach crash, Ken continues to track The Rattler, who has kidnapped his friend Breezy. Realizing that the kidnapping is a trick, Ken races after The Rattler, but is caught in a dynamite explosion.
Ken suspects Dr. Edwards of being The Rattler. Breezy attempts to photograph The Rattler. When he pursues a band of riders, Ken is led into an ambush.
Ken and Breezy head to town to have Breezy's photos developed. On the way, Ken finds The Rattler's disguise hidden among some rocks, puts it on, and pretends to be the villain, eventually getting trapped by the real Rattler.
About to be used as "target practice" by The Rattler's men, Ken is saved by Breezy. They catch up to The Ratter, tell him to unmask, and find out it is a friend, Henderson, who has also found a disguise. They all get trapped in a secret cave.
Henderson is about to reveal the identity of The Rattler when he is killed by a dart. On the pursuit of the killer, Ken and a wagon train are lead into an ambush. One of the leaders of the train (Gene Autry) fires at Ken to get even.
Breezy alerts everyone that The Rattler is posing as Ken. The real Ken is taken prisoner and escapes, only to be caught in gunfire by The Rattler.
Breezy finds The Rattler's closet full of disguises, while the villain poses as yet another person. Ken and Breezy pursue The Rattler to his den.
The Rattler pursues Ken and Breezy, locking them in his disguise room. He kidnaps their friend, Jane.
Ken once again dresses as The Rattler to trap the criminal and save Jane. They are caught in a fight that involves deadly gas and are sent to the hospital.
Ken continues to pursue The Rattler and unmasks him, with the help of Tarzan, just before he is kicked over a cliff.
Tarzan saves Ken from falling over the cliff, and Dr. Edwards is revealed to be The Rattler, but the doctor is only another of the villain's disguises. Ken sets a trap where all of the suspects show up. The evil Frank Blayden is exposed as The Rattler and dies in a mine explosion.
|* Not Credited Onscreen
|Otto Brower, Breezy Eason
|Victor Zobel, Armand Schaefer
|Sherman Lowe, Barney Sarecky, Breezy Eason
|Ben Cohen, Armand Schaefer
|Ernest Williams, William Nobles