When 4400s around the world come down with life-threatening illnesses, Ryland comes back to NTAC and orders the sick - and even unaffected 4400s - to be quarantined. Tom and Diana race to find a cure and discover a shocking secret in the process.

A morbid premonition from Maia threatens the future of the 4400 Center.

A 4400 terrorist releases a signal at NTAC that makes the men violent, forcing a lockdown of the facility. Lilly questions how the Centre is handling her daughter, and Shawn tries to recruit a familiar face.

Tom and Diana investigate a 4400 junior high school teacher accused of child abuse.

Tom and Diana investigate a mysterious structure being built at a psychiatric hospital, based on the drawings of one of their patients who's a 4400.

NTAC is keen to find Jordan Collier's killer as Tom is desperate to find Kyle.

Richard must protect his family when he and Lily are discovered to be 4400s.

A returnee exhibiting telepathic abilities seeks help from NTAC, but is instead used as a mole to infiltrate Jordan Collier's 4400 Center.

A 4400 with the ability to repair damaged chromosomes hides a shocking past. And while Richard seeks out a tormentor among his Korean War buddies, Shawn reconnects with his family and tries to help Kyle.

Tom and Diana investigate a 4400 whose ability to increase the human bodies' metabolism just may be this weight-conscious world's answer to the ultimate fat-burner.

Tom finds himself in a world where the 4400 never happened.

After living for 8 years in an alternate world that only Tom and Alana remember the world with the 4400 has returned as it was at the second the 8 years started. A 30 year old 4400 woman wakes up and finds everybody else in her local community dead. Maia puts April's love for her to a test.

Discovering that NTAC is behind the disease plaguing the 4400s, Tom and Diana try to get to the bottom of NTAC's cover-up, while Kyle considers turning himself in.