When a passing comet abruptly changes course and hurtles towards Earth, there is widespread panic and distress as people prepare for Armageddon. However, the comet does not crash: instead, it slows down, hovers, and eventually touches down on a lake in the Pacific Northwest. Finally, 4400 people emerge from a blinding white light, people from all different ages and walks of life who have been presumed dead or missing - and none aged even a day from when they were last seen. It's as if a giant time capsule full of people has been opened up, unaltered and untouched by time. Although not immediately evident, it soon becomes apparent that The 4400 have each been returned with a special power as they unwittingly begin to exhibit abilities including superhuman strength, healing touch, and clairvoyance. Eager to revisit memories from their past and reunite with those they left behind, two worlds collide as 4400 people acclimated to living in the past are forced to deal with the new challenges of living in the present.

A new federal division agency of Homeland Security called NTAC (National Threat Assessment Command) is formed to follow The 4400. Tom Baldwin, a crime investigator, and Diana Skouris, a bio medic, are one of the many agents. Tom's involvement is personal: his nephew Shawn was one of the 4400 people abducted - and, if not for Shawn, his son Kyle would have been abducted instead.