Government agent Alice Cable (Adrienne Barbeau) is flown into the swamplands to take over as the official representative in the laboratory of Dr Alex Holland (Ray Wise). He needs protecting because certain unscrupulous parties are have an interest in stealing the work Holland is pioneering, and one such party is Dr Anton Arcane (Louis Jourdan) whose troops are making their way through the forest towards the laboratory. When Cable meets Holland, he explains that he is researching a formula that will make plants more like animals so that they can grow in harsh landscapes and conditions, and it looks as if he may have made his breakthrough. What a pity it's all about to come crashing down around his ears...
For a respected director of thrillers and horrors, it's alarming just how many silly films Wes Craven has to his credit, and Swamp Thing, which he scripted from the cult comic book, is one of his silliest. It's as if he was dismissive of the story's origins and decided to make it as camp as possible: there are few who can take this film with any measure of seriousness and if it wasn't for the odd spot of violence ("I'm crushing your head!") and tasteful nudity (courtesy of Barbeau having a bath in swamp water) it could pass as an update of one of those nineteen-fifties mad scientist science fiction movies.
If the film proves one thing, it's how difficult it is to walk around in a swamp. Marvel as the cast struggle to put one foot in front of the other as they stumble their way through the boggy undergrowth, which prompts you to wonder whether they'd rather have made "Beach Thing" instead. Anyway, back to the plot, which sees Arcane and his men invade the lab and kill just about everyone there, including Holland's sister, knocking Cable out and attacking Holland just as he was about to engage in a lightning fast romance with her. Then Holland grabs the secret formula - did I mention it was explosive? - and tries to escape.
It's to no one's shock that he fails, there's a big explosion and Holland disappears into the water. Nevertheless, Arcane is happy because he has the notebooks and journals that spell out the way to make more formula. Ah, but wait a minute, as Cable steals the final book and escapes unseen, hiding it under a tree, meaning Arcane's plans for world domination (isn't it always the way?) are scuppered unless he can catch her. You'll quickly notice a pattern forming as Cable will get away from Arcane's men, be captured, get away once more, then repeat until the film is over. She can't even telephone the government to help, so who can?
Well, in an unconvincing development Holland has mutated into a man in a rubber suit (Dick Durock), the Swamp Thing of the title. He is filmed like some kind of Bigfoot, a mysterious figure whose howls are intermittently heard across the land, and to be honest a Bigfoot would be more believable than what we are offered. There's supposed to be a love affair developing between Cable and her hero who is always on hand to rescue her, but the film's most interesting relationship is between her and the teen gas station attendant she meets while on the run (Reggie Batts gives the best performance). The whole enterprise ends with a big battle between S.T. and a mutated Jourdan (presumably he wasn't in the suit) which makes your average Godzilla movie look persuasive. Who is all this for? Music by Harry Manfredini.