It starts out on an island where two natives fight over the same woman. When one man is killed, the other is punished by becoming a mummy, while his true love's head is cut off and tossed around by the natives. Cut to a shot of a rocket taking off while the opening credits play over NASA photos. HUH?!? "A thousand years later" his coffin is taken aboard a cruise ship by an antiques curator, whose secretary just happens to be the mummy's reincarnated lover (even though now she is mysteriously WHITE!). He wants to make time with her, but unfortunately he transforms from being the shriveled up mummy to being his former suave self at random, which hampers his progress. Meanwhile, he uses his magic ring to turn cruise goers into slaves, decapitates some dude's head and puts it in his woman's bed, and has lots of red tinted flashbacks. In the end, both the mummy and his true love are flamethrowered to death by some trigger happy extra.
The Karloff inspired make-up is actually pretty good, and while the severed heads are really fake looking, they add to the cheese factor. The complete ineptness of this movie is pretty laughable (like seeing crewmembers reflected in a mirror), but you should only check it out if you've never seen a terrible black mummy movie before.