Everyone on Earth is excited about a comet passing by, but as soon as its trajectory changes to a collision course, everyone starts to panic. The comet turns out to be a giant ball of light that, after exploding, leaves behind 4400 people. They are missing persons who have been gone from a few months to 60 years, and none have aged a day. The 4400 are put in quarantine and eventually released. Some of the returnees begin to exhibit strange and uncontrollable new abilities. Tom Baldwin and Diana Skouris, two Homeland Security agents, are appointed to find out what happened to the 4400.