In the fourth-season opener, the NTAC deals with a new director and a high-school student who developed a special ability after taking promicin. Meanwhile, Tom (Joel Gretsch) visits Isabelle in prison and Diana searches for her sister, who took promicin.
Tom and Diana look for a person who makes phobias all too real. Meanwhile, Kyle gets another lead from Cassie, this time to a book that contains a prophecy about Collier.
An elderly woman develops the ability to astral project unseen by others, but she is stuck in limbo when her body is murdered, and she must find a way to contact Tom and Diana to help catch her killer. Elsewhere, Shawn decides to start healing people again despite threats.
Diana finds her sister, whose life is in danger due to promicin. Elsewhere, Shawn considers a run at public office.
Tom tracks down Collier, who is living in a small town with his followers. Meanwhile, Maia has a disturbing glimpse of the future.
Collier tries to persuade Shawn to join his movement. Meanwhile, a 4400 who knows the truth behind historic conspiracies goes missing, prompting a search by Tom and Diana.
Assassins target Jordan Collier after his movement gains momentum. Meanwhile, Shawn encounters trouble in his run for public office. Kevin Tighe guest stars.
A lockdown at NTAC traps everyone, including Collier and his group, forcing an unlikely alliance.
Richard kidnaps Isabelle from Promise City in hopes of starting over. Meanwhile, Shawn is asked to intervene after Tess takes over a diner.
Tom and Diana look for Richard, but Tom is distracted by his dreams about the future. Meanwhile, Collier is threatened by Shawn's test that could determine who would die from a Promicin shot.
A computer virus attacks a large software company owned by a suspected member of the Marked. Elsewhere, Maia visits Promise City and receives an unexpected birthday gift.
Meghan and Diana learn how to remove the entity from Tom, but the procedure is dangerous. Meanwhile, Shawn finds help in his attempt to rescue Kevin from Promise City; and Jordan is betrayed by someone close.
Season 4 ends with Seattle in chaos and NTAC asking Promise City for help. Meanwhile, Kyle's life is in danger and Jordan attempts to escape from the Marked.