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

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

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.

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.

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.

Paramedics try to resuscitate Susan Farrell. They believe that she took promicin and lost the 50/50 lotto that comes with it. Danny is certain that she did not take the shot. After arriving at the hospital with the paramedics, things get complicated as everyone around Danny start to die. Garrity and another NTAC agent are sent to the hospital to assess the situation.

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

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

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.

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

Jordan Collier's movement takes a huge step forward when his followers settle in the heart of Seattle.

Tom and Diana investigate Oliver Knox, a 4400 suspected of being a serial murderer.

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

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.

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

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

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

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

Tom and Diana's investigation into a series of gruesome murders leads them to uncover another conspiracy within the government. At the 4400 Center, Shawn receives a gift from another returnee that allows him to see his future.

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.

Gary Navarro is arrested for the second attempt to assassinate Dennis Ryland. Knowing she is the key to her mother's survival, Isabelle attempts to kill herself by jumping off the 4400 center building only to survive without a scratch. Matthew Ross expresses his displeasure at her actions and tells her of the destiny she is to face. Isabelle is troubled about what Matthew told her, but after a discussion with Shawn she decides it's her choice with what she does with her life. Matthew gives Isabelle a substance that can kill her if it's injected.

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.

Ryland and other government officials are on trial for withholding vital information that they discovered about the returnees when a disturbing sound is heard the courtroom. Tom and Diana, with the help of Gary Navarro, try and track down T.J Kim, who they believe is responsible for the piercing sound heard in the courtroom. Richard and Lily are forced to deal with a now grown Isabelle While Lily also suffers from a rapid aging disease that Shawn is unable to heal. Tom and Diana also investigate a radical organisation called the Nova Group that appears to have ties with Shawn and the 4400 Center.