A mad scientist named Dr. Satan plots to steal key pieces of technology to enable him to build an army of robots based on his prototype to conquer America. The only one standing in his way is Bob Wayne, who fights Satan as the enigmatic Copperhead. Mysterious Doctor Satan is a 1940 film serial named after its chief villain. Doctor Satan's main opponent is the masked mystery man, "The Copperhead", whose secret identity is Bob Wayne, a man searching for justice and revenge on Satan for the death of his step-father. The serial charts the conflict between the two as Bob Wayne pursues Doctor Satan, while the latter completes his plans for world domination.

Return of the Copperhead: Doctor Satan's henchman remotely blows up the experimental ship, with Lois and crew aboard, as ordered.

Copperhead is electrocuted in Doctor Satan's lab as he captures the Doctor and his thugs.

Copperhead drives into a sheet of flames and his car explodes

A depth charge explodes. The diving bell, containing Bob & Lois, cracks and begins to fill with water.

Copperhead is caught in the crushing grip of The Robot.

Lois is bound and gagged, the door handle is rigged to electrocute the Copperhead if he attempts a rescue, and poison gas is set to be released by a timer.

Splashed acid burns The Robot's circuitry and sends it out of control. It topples a case of acid on itself and the stunned Copperhead.

Copperhead, fighting on the back of a truck, is knocked off the vehicle. Speed, pursuing in a car, runs him down.

An open can of gunpowder is knocked over when a fight breaks out in a mine. An escaping thug knocks a lit torch onto the trail which in turn sets off all the explosives.

During a chase across a gas works, Copperhead is knocked from a narrow beam by a block and tackle swung at him.

Doctor Satan drops the Copperhead through a trap door and activates a sliding wall in the cell beneath to crush him.

An aircraft being flown by Copperhead crashes into a mountain.

As the Copperhead leads escapees round a corner, Joe the thug opens fire on them, and the leading figure falls, shot.

Copperhead hides in a box about to be delivered to Doctor Satan's new hideout. Doctor Satan suspects a poison gas booby-trap and has the still sealed box incinerated.

Doctor Satan Strikes: Copperhead had already left the box when the delivery truck parked, substituting sacks of ore to maintain the box's weight.