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.

While Swamp Thing senses a growing darkness within the swamp, Abby’s return dredges up her dark history with the Sunderlands. We learn more about the mysterious Dan Cassidy.

While Swamp Thing finds a new way to communicate with Abby, Matt learns the truth about Alec Holland and Avery pressures Woodrue to deliver results.

While Maria meets with the shadowy finance group known as the Conclave, Lucilia leads Avery out into the swamp under false pretenses.

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.

While Abby and Liz track down the secret Conclave facility, Jason Woodrue conducts experiments on Swamp Thing and makes an incredible discovery.

Still reeling from the revelation of the truth behind his existence, Swamp Thing goes on the offensive against Ellery's mercenary team hunting him; Abby comes up against Jason Woodrue, who has crossed the line to save his wife's life.