Donald Blake has just finished treating Thor -- or rather a strong man who dresses as him as part of a circus troupe. He finds that the strong man had injured himself lifting something very heavy. However, unfortunately for the inquisitive mind of Donald Blake, this circus happens to be the one owned by the Ringmaster, leader of the Circus of Crime, who promptly dismisses the questioning doctor. Recognizing the Ringmaster from their previous encounter, Donald Blake decides to investigate the situation as Thor.

While in far off Asgard, Loki has gathered a band of malcontents who wish to overthrow Odin and defeat Thor. Among their numbers is the Rock Troll Ulik, who wishes to get revenge against Thor. Finding Ulik a fitting tool against Thor, Loki transports the Rock Troll to Earth, sending Ulik to the circus where Thor now stalks. Ulik's sudden appearance and demands for Thor to appear to bring the Circus of Crime, who all try to attack him and are easily defeated. When the Ringmaster arrives, he easily puts Ulik into his thrall using his hypnotic hat.

When Thor stumbles upon the scene, he is spotted by Princess Python, who mistakes Thor as the strong man who pretends to be Thor as part of his act. Thor uses this to his advantage to find out what the Circus of Crime is up to. Participating in the act, Thor is shocked to see that Ulik is present and under the Ringmaster's control.

When Ulik is commanded to lift a one-ton weight and put it on a flatbed truck, Thor realizes that this must be part of the Ringmaster's scheme. Thor then rouses Ulik out of the Ringmaster's thrall, making Ulik drop the weight and turn his attention against Thor. After a brief battle, Thor uses the magic of his hammer to banish Ulik back to Asgard.

With Ulik gone, the Ringmaster attempts to put Thor under his control. However, the Thunder God anticipates this move and knocks off the Ringmaster's hat. The police arrive, and the Circus of Crime is rounded up and taken into police custody. When the Ringmaster demands proof of wrongdoing, Thor smashes open the weight revealing that it has a stolen defense computer within.

As police are escorting the Circus of Crime members, Princess Python asks Thor why he wouldn't get in league with them as they would have paid him well to go along with their scheme. Thor responds that his actions are never a consideration of monetary gain and that of truth and justice before departing.

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