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.

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.

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

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.

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.

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

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.

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.

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.