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.

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.

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

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.

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

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

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

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.

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.

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

NTAC races against the clock to stop a group of fanatics targeting 4400s.

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.

Kevin is on the run after horribly mutating due to the promicin experiments. Tom and Diana go to Tess for help. Diana gets what she believes is the flu and discovers something startling.

NTAC and the 4400 Center work together to find Jordan Collier. Kyle Baldwin gets a surprising visitor at the state prison.

A high school student develops an ability after injecting promicin. Tom visits Isabelle in jail, while Diana searches for her missing sister. Following the advice of a young woman, named Cassie, Kyle is able to wake Shawn from his coma. Jordan Collier's conscience gets to him. Meanwhile, NTAC gets a new director.

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

Tom and Diana investigate a 4400 who has used his ability of enhanced reflexes to become a vigilante.

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.