A defecting Russian scientist is transformed by an atomic test into a hulking monster (Tor Johnson, of course). Not much else except some people are killed, boys get lost, and a rabbit sniffs Tor’s corpse. This film was used for Mystery Science Theater 3000.
It has been speculated that this film was the partial inspiration for the “Incredible Hulk” comic book that came out a year later. The stories and certain plot points are very similar