Alec and Linda Holland are husband and wife scientists taken to the Bayou by government agent Matthew Cable so they can work in secret on their bio-restorative research. It's not long though before a man called Ferrett arrives at the isolated house.He attempts to acquire the Hollands research on behalf of an organization known as The Conclave. Alec refuses and Ferrett and his henchmen leave.
It's not long though, before Ferrett returns with orders to kill the Hollands and destroy the restorative compound. There is a struggle during which Alec is knocked out and when he recovers he finds a bomb planted in the lab. Attempting to flee he is caught in the blast and then stumbles on fire into the swamps surrounding the house.
We then see Linda Holland and Matthew Cable at the funeral for Alec, but Cable is determined that the project must continue and returns Linda to the rebuilt lab in the Bayou. Far from being dead though, Alec emerges from the swamp altered, by a combination of the explosion and the restorative compound, into the creature known as Swamp Thing.
Back at the lab Ferrett arrives yet again, to make another attempt to acquire the compound. Cable is beaten unconscious and Linda is threatened. Alec, in his mutated form, arrives too late and finds Linda murdered. In a rage Swamp Thing chases down Ferrett and his thugs and kills them. Now recovered, Cable sees Swamp Thing and shoots at him but he shrugs off the shots and returns to the swamp. Not realizing that Swamp Thing and Alec Holland are one in the same, Cable vows to bring him to justice for murder.