"A hydra is threatening the countryside and the people are terrified for their lives. The people's only hope of survival rests with Maxus, a powerful man who has the strength of many men. Before Maxus can battle the multi-headed monster, he must face other challenges in order to prove himself worthy and to prepare for the fateful battle," according to the DVD sleeve's synopsis.
Actually, the story mainly involves a struggle between two pre-historic tribes: the "Good" or "Sun" worshipers, and the "Bad" or "Moon" worshipers. The "Sun" tribe of Nomads has decided to settle and live in peace; but, they pick land claimed by nearby "Moon" worshiping Cavemen. Bodybuilder Reg Lewis (as Maciste, or Maxus in English) does not belong to any tribe; however, he bonds with "Sun" leader Luciano Marin (as Idar), after saving him (and his woman) from a sea monster. The plot thickens when Mr. Lewis and "Moon" tribe woman Margaret Lee (as Moah) fall in love.
In English, misleadingly reproduced as "Fire Monsters Against the Son of Hercules". The English dubbing is dreadful; in a couple of scenes, two completely different voices dub Lewis. The bleached-blond muscleman throws cavemen around, and poses. Mr. Marin essays his part better than others; but, considering the shoddiness of the production, it's a wasted effort. The best part of the movie is the added-on TV theme song, "The (Mighty) Sons of Hercules".
*** Maciste contro i mostri (4/25/62) Guido Malatesta ~ Reg Lewis, Margaret Lee, Luciano Marin