When Moretti goes missing the day of her wedding, Pierce and Donnie set off in pursuit of the runaway bride. They soon learn that Kate has been abducted by a dangerous person from Pierce's own past. Now, Pierce and Donnie must risk everything to save Moretti before it's too late.
When a student is found murdered, Pierce tries to find the killer while defending the victim's boyfriend; Pierce must confront his feelings as Kate and Donnie prepare for their wedding day.
Pierce and Moretti uncover an international scandal while investigating the murders of a Bangladeshi diplomat and a Chicago reporter; Moretti struggles with the preparations for her upcoming wedding.
Agent Kate Moretti goes under cover to investigate an animal rights group suspected of foul play; Pierce considers making a confession to Kate.
After Dr. Daniel Pierce suffers a traumatic injury, his father and his friend must decide if they should allow him to undergo a high-risk surgery; Pierce begins to question everything he sees and hears.
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.
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.
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.
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.
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.
When renowned neuroscientist Landon Jennings is found dead, Moretti and Pierce must figure out how someone could have gained access to his impenetrable study in order to kill him. Lewicki finds himself with twice the work when Pierce’s father James moves in with them.
Moretti calls on Pierce to examine Elena Douglas, a woman who has confessed to murder and claims to be possessed by the Devil. Meanwhile, Donnie and Moretti’s wedding plans hit a bump in the road.
After a young victim with a developmental disorder is taken hostage in a bank robbery, Moretti brings in Pierce to interview the boy. When they finally track down the culprits, they discover the case is about much more than money. Meanwhile, Pierce’s estranged father James pays him a visit.
When a prosecutor mysteriously drops dead in the middle of a courtroom, Pierce and Moretti go on the hunt for a killer. Meanwhile, Moretti and Donnie make some decisions about their future.
Dr. Daniel Pierce’s picture-perfect new life in Paris is suddenly turned upside down after he is approached by the FBI legat to help with a dangerous international case. Meanwhile, his assistant Max Lewicki and Dean Paul Haley plot to get Pierce to return to Chicago.
