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

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.

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

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.

Diana helps Tom break Kyle out of NTAC quarantine, eventually leading them to discover the truth behind the 4400.

NOVA group members that were in the custody of NTAC escape from jail with outside help from Jordan Collier. Diana tells April about her relationship with Ben. Shawn and Richard learn that Isabelle is working with Dennis Ryland.

4400 people, assumed to be dead or missing over the past fifty years, reappear in a ball of light. None have any memory of where they've been, and some are manifesting paranormal abilities.

Tom and Diana continue to investigate the disappearance of the 4400 children. Isabelle and Shawn's relationship becomes public.

Tom and Diana continue their investigation on Jordan Collier's plan for mankind. Dennis Ryland rejoins NTAC. Isabelle prepares for battle.

Someone is targeting young 4400's and Maia gets kidnapped. A mistake from Shawn's past comes back to haunt him. Richard is given a position of authority at 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 Oliver Knox, a 4400 suspected of being a serial murderer.

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

Tom has trouble focusing on the hunt for Richard Tyler because of dreams he's having about the future.

Tom and Diana are drugged with a hallucinogen, that was created from oil that was secreted from the hands of a 4400.

Richard surprises Isabelle when he shows up in Promise City but the happy reunion takes a turn when Richard kidnaps her in hopes to start a new life with his daughter.

Isabelle seeks revenge on the Nova Group after they attack Shawn. Alana confronts the man responsible for killing her husband and son in a car accident nine years ago.

Diana locates her sister, April, who took promicin and developed an ability that puts her life in jeopardy.

Tom, Diana, Jordan, Shawn, Kyle, Isabelle, Maia, Meghan, Marco, PJ and Brady all wake up inside NTAC without any memory of how they got there.

Tom and Diana must race to find the source of a computer virus that could bring down Ubient software, one of the world's largest software companies that is run by suspected member of the marked, Drew Imroth. Meanwhile, Maia visits Promise City where she receives an unexpected birthday surprise: a visit from her birth parents.

With the help of Dennis Ryland, NTAC track down the remining members of the NOVA group. Nikki pays Shawn a visit.

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.

Jordan wants Shawn to rejoin the movement. Meanwhile, a 4400 with an amazing ability disappears.

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.

Tom and Diana search for someone who has the ability to make people's worst fears come true. Danny seeks Shawn's help to find a promicin shot. Meanwhile, Cassie leads Kyle to a book that contains a prophecy about Jordan Collier.

Tom is accused of murdering TJ Kim. 17 year old Boyd Gelder has the ability to change his appearance whenever he chooses. Meanwhile, Shawn and Isabelle grow closer.