Mill Creek actually claim this as two of the 50 films in this pack, presumably due to length. As a compilation of a 12-part serial (pretty much without cuts, as far as I can tell), it runs nearly three and a half hours. I'm going to treat it as just one film, though. Partly because it's clearly intended to be viewed as a single narrative, and partly so I don't have to write two reviews of this piece of junk.
Strange electromagnetic phenomena are wreaking havoc in the world, but handsome and dashing young electrical engineer Bruce Gordon traces the source of the disturbance to an isolated part of Africa. I'll just mention that Flash Gordon made his newsprint debut the year before, and leave you to ponder any parallels between the two.
Gordon heads off to deepest, darkest Africa to uncover what's behind the disasters. There he uncovers the Lost City, ruled by Zolok, Last of the Lemurians. Zolok proudly proclaims his people's mastery of all things electromagnetic, but it seems the most marvelous creations in his possession are actually all the work of a Dr Manyus, whose obedience Zolok ensures by holding the Doctor's daughter hostage (do you smell a love interest for Gordon? Of course you do.).
As an aside, it's worth noting that the actor playing Zolok appears to be more hammered than Michael Madsen in Bloodrayne in at least one scene. This would not be surprising, as he was regularly arrested for alcohol offences during prohibition.
Anyway, the good guys escape from Zolok and his minions around the 60 minute mark, and spend all but 20 minutes of the remaining two hours blundering around the jungle encountering various people who want to co-opt Dr Manyus's inventions for their own ends.
What are those inventions? All sorts of nonsense, frankly. Manyus can transform ordinary men into giants, and black men into white (oh yeah, there's some major, major racism in this: "That sounds like a white girl's scream!" being one of the more absurd examples, with bonus misogyny added in for good measure).
Eventually - and I do mean eventually - they end up back at the Lost City, overcome Zolok, and save the day.
So dull, I need a pick me up. Only one thing for it.