Let me set the scene for you. This movie is called Neutron and the Black Mask, but neither Neutron (our hero) nor Dr Caronte (our villain) wears a black mask. There is one scene where Neutron wears a black mask (and calls himself The Black Mask), but it’s literally only one scene in the entire film.
The proxy struggle between Neutron and Dr Caronte in this film involves a scientist who invents a bomb so incredibly powerful that it will guarantee peace. You can imagine how well that works out.
The scientist’s evil lab assistant kills him in order to steal the formula. Dr Caronte wants to buy it. Neutron doesn’t want Dr Caronte to have it. The usual policia are their usual marginally-competent-but-not-so-much-as-to-overshadow-the-protagonists selves.
There is also a bit of plot involving the daughter of the lab assistant, who is as noble as her father is treacherous. Coincidentally, she is also quite pretty!
The Neutron movies are fairly interchangeable, and this is, without question, the first one. Apparently the US version removed most of the musical numbers from this movie, and I have to live with that. And so do you. Somehow.