Pierce and Moretti race to find clues when a serial killer from 1986 begins killing again. They catch a break when they learn that one of the victims is actually alive. Moretti's dad, one of the investigators on the original case, offers his daughter advice. Pamela Reed also guest-stars as the mother of the surviving victim, while Armin Shimerman is the victim's psychologist.
When a young man in a cult claims to be hearing the word of God, Pierce must determine if it's actually the word of God or a life-threatening neurological condition. Pierce and Moretti must also figure out if his murder is linked to his drug past or his new life with an organization that may be scamming people out of their life savings. Roger Bart guest-stars as Ethan Kendrick, a high-powered IRS agent looking into the finances of the organization. Meanwhile, the university gives Pierce an award for his research.
Pierce must take a deep look into his own life when he is brought into a case involving a schizophrenic. Meanwhile, Moretti stops at nothing to impress her new boss at the FBI. Guest star Tom Sizemore plays a top-level Irish mobster, while guest star Edward Furlong plays a would-be tough guy who may have played a crucial role in the crime.
Moretti and Pierce are called upon to solve a crime in their own backyard when a college student is killed in her dorm room. Pierce is forced into the uncomfortable situation of interacting on a personal level with more than one of his students, which forces him to confront difficult truths about his own past. The case comes just as Moretti is beginning to re-evaluate her relationship with Dr. Hathaway.
FBI Agent Kate Moretti asks Dr. Daniel Pierce to determine the mental competency of a man being retried for murder. But the trial takes a shocking and unexpected turn when Pierce’s findings question whether the person standing trial is the same person he was six years ago. Meanwhile, Moretti is unpleasantly surprised to discover that the Assistant U.S. Attorney prosecuting the case is her soon-to-be-ex-husband Donnie Ryan.
Pierce and Moretti take on an extraterrestrial case when a woman reports that aliens have abducted her husband. When Pierce and Moretti arrive to investigate, however, they make a startling discovery. Meanwhile, things heat up between Pierce and his real-life girlfriend, Caroline, but his relationship could be jeopardized if he can't get his imaginary girlfriend, Natalie, out of his mind.
When a series of bizarre public murders occur, Pierce realizes that the killer is trying to send a message about inattentional blindness, but Donnie doubts this theory. But Pierce has a trick up his sleeve that can prove his point, and they must scramble to piece together the clues before the clever killer can make any more examples out of innocent victims.
Pierce accepts an invitation to work on a case from a renowned environmental activist concerning a chain of abnormal neurological reactions in a group of young girls. However, upon examining the girls, Pierce discovers that a dark secret is at the root of their ailments. Meanwhile, Moretti questions Pierce’s motives in working on a case without her.
Pierce and Morretti plunge into virtual reality to solve the murder of Kurt Simpson, a man who spent most of his time in a massive multiplayer online game called Caleidoscope. After creating an avatar of himself to investigate the crime, Pierce struggles more than ever to distinguish between reality and fantasy.
A new brain device to control tremors seems to have a defect that turns out to be far more serious than a technical malfunction, and Pierce partners with Donnie to investigate. Their unlikely alliance is tested when the case escalates to murder. Meanwhile, Lewicki learns a valuable lesson about dating.
When Moretti receives a deathbed confession about the hit-and-run murder of a teenager from 1992, she calls on Pierce to determine the ailing man's credibility. The case becomes complicated, however, when the alleged killer's physician, Dr. Hutchins, reveals that his patient’s tumor has mysteriously disappeared. Pierce and Moretti must dig deeper into the past to uncover the truth behind a shocking series of apparent homicides.
Pierce and Lewicki are caught off guard when Lewicki’s brother Kenny shows up unannounced. In an unwelcome turn of events, Kenny is named the key suspect in a homicide case, leaving Pierce torn between helping a friend and serving justice. Meanwhile, Lewicki is approached with a tantalizing offer that makes him question Pierce’s loyalty to him.
When an infant is reported stolen, Moretti hunts down the kidnapper and makes a very bizarre discovery. As Pierce and Moretti investigate a related murder, they find that there might be another child out there who needs their help. Meanwhile, Donnie and Moretti discuss their future together when Donnie looks into buying a house in the suburbs.
After Pierce witnesses a gallery owner die during a seizure caused by a video installation, he convinces Moretti that it was actually a murder. Their search for the killer puts them in the middle of a brazen art heist. As Pierce works on the case, he is forced to re-examine his relationship with Natalie.
After a missing FBI agent turns up dead, Pierce is forced to face the one case he was never able to solve. When they discover that the killer is still out there, Pierce agrees to help Moretti, against the wishes of his therapist, Dr. Rosenthal, who believes it will only exacerbate Pierce’s condition.
Donnie and Moretti are caught in the crossfire when a sniper shoots up the lobby of the Federal Building. When Pierce determines that the shooter is afraid of Extreme Low Frequency radio waves, he and Moretti take a trip to the Quiet Zone in Virginia, where they think the shooter is hiding out. Meanwhile, an alluring woman named Shelby Buchanan courts Donnie to run for political office.
When Donnie finds himself in a compromising situation, he calls Pierce for help. As the evidence begins to stack against Donnie, Pierce and Moretti struggle with their own fears and doubts, as they work to solve the case. During the chaos, Pierce must deal with his father after he assaults someone at the assisted living facility.