Something unnatural is happening in the swamps outside Marais, Louisiana. When a mysterious illness strikes the town, CDC investigator (and former Marais native) Abby Arcane is sent to investigate.

Certain that Alec's disappearance is more than an accident, Abby and Matt venture into the swamp, where she encounters Swamp Thing. Scientist Jason Woodrue comes to Marais.

When her friend and co-worker is stricken with the green flu, Abby searches Alec’s lab for a cure, but instead finds the latest supernatural reanimation from the Rot.

After a harrowing journey of survival through the swamp, Avery comes face to face with Swamp Thing, who rescues the injured man and helps his recovery.