CDC investigator Abby Arcane is sent to investigate a mysterious illness in Marais, where she and Matt encounter a creature born of the depths of the swamp's terrifying secrets.
Abby and Matt follow one of her patients into the swamp, where Abby encounters Swamp Thing; Alec struggles to understand his metamorphosis into the monstrous, plant-based creature, Swamp Thing.
Alec is haunted by what he has done as the Swamp Thing. As the mysterious disease continues spreading through the town of Marais, a new menace crawls from the swamp.
Abby's return to the town drags up her dark past with the Sunderlands. While the Swamp Thing senses a growing darkness within the swamp, we learn more about Daniel Cassidy.
While Abby tries to find a cure for Alec, she's haunted by her childhood friend's ghost who re-emerges from the swamp. Alec struggles to come to terms with his transformation with the help of a mysterious Phantom Stranger.
Still taking in on his human appearance, Swamp Thing takes Abby to a rotten part of the swamp where she gets in danger. Lucilia leads Avery to the swamp with a hidden intention, while Maria meets up with a leader of some shadowy group.
After a harrowing journey of survival through the swamp, Avery comes face to face with Swamp Thing, who rescues the injured man; after recovering, Avery vows to return with Woodrue to help find a cure, but they may not be able to be trusted.
