The movie follows the story of John Bentley, a police doctor who starts working on the case of a series of brutal murders in the city. The victims all die from their spines being broken by brute strength, and despite being shot by police, the killers walk away unharmed.
Bentley soon discovers that the murders are being carried out by an army of criminal musclemen who have been brought back to life through a scientific experiment. The experiment is being controlled by a former crime boss, Frank Buchanan, who seeks revenge against those who wronged him in the past. He teams up with a former Nazi scientist, Dr. Wilhelm Steigg, who has developed a method of reanimating dead tissue using atomic energy.
Together, they use the dead criminal musclemen to carry out a series of violent attacks on their enemies. However, when Bentley starts to get too close to the truth, Buchanan and Steigg decide to target him as well.
The movie climaxes in a thrilling showdown between the police, Buchanan, Steigg, and the army of reanimated criminal musclemen. Bentley and the police manage to destroy the laboratory, killing Buchanan and Steigg in the process, and bringing an end to the deadly experiment.
Overall, Creature with the Atom Brain is a classic sci-fi thriller full of suspense, action, and horror, and is considered a cult classic by fans of the genre.