This somewhat dull B-movie is notable mainly for two things: the presence of Boris Karloff in the lead role and also an uncredited appearance by a young Adam West in his first role on the screen. The premise is not particularly innovative: a wealthy developer has sent a team to explore an island and only one of them makes it back alive, and he has apparently become a zombie. The developer sends Phillip Knight (Karloff), a professional debunker, to investigate. This is one of those movies where you can't ask too many questions, like: If the developer thinks there's something strange going on, why is he sending a debunker? Apparently so we can see the debunker become a believer in the supernatural by the end of the movie.
Traveling with Knight are his frigid assistant Sarah (Beverly Tyler), some crony of the developer and his assistant, and the zombie from the first exploration. On the way to the island they run into freak radio interference and odd weather patterns, a la Bermuda Triangle. Once they reach the island, they're also accompanied by the ship's captain from the last leg of their journey, Matthew Gunn (Rhodes Reason), as well as the owner of a nearby resort (Elisha Cook, Jr.). Reason is the stereotypical B-movie tough guy. He sounds like the character that Troy McClure from the Simpsons was based on. Predictably, he and the frigid assistant Sarah fall in love. I won't go too much into their adventures on the island, but suffice it to say that there is actually no voodoo, unless the power of voodoo is to cause people to lose their minds when they see Scary Things. Most of the danger comes from various carnivorous plants.
It's not a bad movie, particularly, it just has nothing really to offer. The performances are adequate, with the exception of Karloff, who is a little better. He sometimes seems to be acting in a better movie than that which he's actually in. The zombie count is a grand total of two, and I would call them the classic voodoo zombies except that they're not, really. You'll have to watch the movie to see what I mean, but it may not be worth your time to find out.