Mental patient David Haller struggles to see what is real after an encounter with a fellow patient named Sydney leads to a catastrophe, sending David on the run and into the hands of a clandestine organization that is looking to capture mutants.

At a secluded compound David's new friends help him to explore his memories, exposing the brokenness of his past and his desire to forget -- while the hunters from Division 3 discover a way they might draw him out.

Although David is distracted by the capture of his sister, Dr. Bird and Ptonomy Wallace press him to explore the major milestones of his powers -- leading to dark corners of his psyche that they did not anticipate.

With David trapped in a coma Syd and the others struggle to find a way to find him and help him escape from his own mind. While they go in search of David's former girlfriend -- in order to read her mind -- Dr. Bird makes a connection with someone from her past.

When David returns from the astral plane with a plan to rescue his sister -- as well as news of Dr. Bird's lost husband Oliver -- Bird worries that he has grown over-confident. Meanwhile Sydney and David explore a new frontier for their relationship.

Trapped inside the mental hospital, David and his new friends have no idea that the reality in which they are living is not real. But as Lenny maintains a tight control over them all, Syd begins to see flaws in her world.

As their fantasy world begins to fracture Cary meets Oliver in the ice cube, where the two try to devise a plan to save everyone. David's monster -- the "Shadow King" -- probes for a secret that David has hidden, while Syd sets out to free him from a prison in his own mind.

David and the others must deal with the watchful eye of Division 3 after an old adversary returns. Cary and Oliver look for a way to extract the Shadow King from David, knowing that it will not go without a fight.