Slugger Sykes and the scientist Chuda are working together to find a means to destroy Thor. At Chuda's lab, Slugger amuses himself by beating up one of Chuda's replicas that were designed to resemble Thor. After the demonstration, Chuda shows Slugger his latest invention: Replicus, an android that can adapt to any situation and hypothetically defeat Thor in battle. Chuda activates the robot, and the two prepare it for its mission to destroy Thor.

Elsewhere in the city, the Thunder God is making a house call to Granny Gardenia in his mortal guise of Donald Blake. As Blake is checking up on the elderly flower vendor, she is visited by some of Slugger Sykes' men, who have come to check on her because Slugger would regularly purchases a fresh Gardenia every day from her. Although Blake recognizes Slugger's name, Granny Gardenia is completely oblivious to Slugger's true vocation, and Slugger's men give Blake grief over ensuring that Gardenia returns to her proper health.

After Slugger's men leave, Granny asks that Blake turn on the television. Upon doing so, both see a news report about Replicus, who had just successfully robbed a bank and managed to escape despite the police efforts to stop the robot. The robot returns to Syke's hideout and dumps the loot, making their first attempt successful. When Sykes' men ask for a money cut, Sykes has Replicus toss them out.

Thus begins a series of crimes by Sykes, who sends Replicus to do all the dirty work. After enough robberies, Blake decides to do something, changes into the Mighty Thor, and searches for the machine. Thor finds it all right, and the two lock in combat. Thor finds to his surprise that the robot can adapt to any situation and exhibits new powers to counteract any attack that Thor throws at it.

As the battle rages on, inside the lab at Chuda, Chunda explains how he will use the Replicus robot to crush democracy. Despite being a crook, Slugger is a Patriot and refuses to allow the robot to be used to destroy Democracy. In the ensuing struggle, Chuda's devices are damaged and explode, killing both men.

With the robot's control devices destroyed, Replicus' attack on Thor ends before the robot manages to lift Thor's hammer. Later, back in his civilian guise of Donald Blake, Thor finds that Granny is doing better but is saddened by the death of Sykes. Blake leaves, musing that Sykes may have died a nobler man than he lived.

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