Season 4 begins with the aftermath of the explosive Season 3 cliffhanger involving a group of terrorists. Cases involving abused children, a cop killer, a modern day Road Warrior, and an Unsub who copies the murders of famous serial killers are just some of the high points of a truly dark season. On a personal level, JJ gives birth and goes on maternity leave, Reid works a case that takes him back to his childhood, and Hotch has another encounter with The Reaper. Noteworthy Season 4 guest stars include Jason Alexander ("Masterpiece") and Luke Perry ("Minimal Loss").
Hotch's SUV explodes leaving Kate (the head of the NYC’s FBI office) seriously injured. Hotch fights to keep Kate alive as the team tracks down the terrorists responsible for the bombing. They discover the bombing is a diversion so that the terrorists can carry out an assassination of a VIP undergoing medical treatment at a nearby hospital.
Recent murders are linked to a serial killer who was executed a year ago. The team determines that a woman who was in love with the deceased serial killer is completing his work as a testament to her love for him.
Prentiss and Reid go undercover with Child Services, to investigate possible abuse charges of children in an underground cult and get caught inside the compound when a federal raid goes bad. They have to help the team from the inside as they try and resolve the ensuing hostage situation with the extremely charismatic cult leader. Luke Perry guest stars at the cult leader.
The team tracks down an UnSub who abducts, tortures, and kills couples who frequent his motel in a resort area. Agents Morgan, Prentiss, and Hotchner raid a roadside motel that maybe the site of a couple's kidnapping. Wil Wheaton guest stars as a motel manager.
The BAU is called in when a series of killings occur in rural areas around railroad tracks. Their investigation leads them to a homeless train jumper riding the rails. This Unsub murders couples and then spends days in their homes absorbing their lives.
A serial killer abducts a child, keeps him alive for seven days then smothers him to death. The team is called in when another child is abducted. They discover and stop the perpetrator of the crime -- a woman who went insane when her newborn infant was taken from her seven days after giving birth. On a parallel track, Reid is plagued by dreams of a murder from his childhood (finding a murdered child in his basement). At the end of this episode, he "completes" the dream and realizes -- or so he thinks -- that it was his estranged father who killed the child in his dreams.
This is the conclusion of the two-parter that began with "Instincts," when Reid was plagued by dreams of a murder from his childhood. He believes that his own father was a serial killer who's still at large. Reid and the team not only profile and locate the correct killer, they put to right this miscarriage of justice from Reid's childhood.
An Unsub presents himself to the team and reveals to them that he is a serial killer who has murdered seven women over the years and at this moment has five other victims who will die in less than ten hours unless the team can stop him. The team must "reverse" profile from a known UnSub to try and find these five victims before they are killed.
The team tracks down a serial killer who preys on beautiful, moneyed, privileged, young women that he picks up at nightclubs. On the personal front, J.J. gives birth to a baby boy.
A BAU case hits close to home for Morgan, who was a cop before joining the team, when a serial killer specifically focuses on members of the police force in Phoenix, Arizona.
The team investigates the murders of "The Road Warrior," an UnSub who kills blonde women driving luxury cars on the Southern California freeways.
The BAU arrest an UnSub who rapes then kills his female victims. During interrogation, the team discovers that this UnSub has a partner and that he's the UnSub's next door neighbor.
The BAU team becomes involved in the case of a family working together to abduct young women.
The team tracks a killer who abducts, kills and embalms his victims. Cybil Shepherd guest stars as Mrs. Gless, the mother of a suspect in a murder case.
The team pursues a copycat serial killer who is recreating the techniques used by past famous murderers.
The team tracks a female UnSub, a high-class call girl, whose victims are captains of industry.
The BAU investigates a series of deaths that were the result of exorcisms. Agent Prentiss has a personal connection to one of the victims in a series of deaths with religious overtones.
Hotch is summoned to South Boston to the deathbed of a detective who headed the first case Hotch worked in the BAU. The dying cop confesses that he made a secret deal with the serial killer. If he stopped looking for the UnSub, the UnSub would stop killing. For ten years both parties observed their unique contract. But now, when the death of the detective triggers the return of the UnSub, Hotch and the BAU must travel to Boston to apprehend the most notorious serial killer in New England's history.
The BAU must track down a serial arsonist/murderer who instills fear in a small town by setting fire to community meeting places and killing several residents in the process.
The team travels to South Padre Island during spring break to track down an UnSub with multiple personalities who as a woman seduces her victims (college frat boys) but then as a man, rapes and murders her/his victims.
When profiling a series of child abductions and murders, the team discovers that one of the cases is not the handiwork of the serial killer they apprehended.
An UnSub has sent the BAU edited film footage of him going about his day, including the murder of one of his victims. Upon closer look, the team also discovers a message written by the UnSub, “Help Me.” The team uncovers the real reason this UnSub wants to be stopped before he kills again, he has formed a personal attachment to the blind child of one of his victims.
Local authorities summon the assistance of the BAU after a series of homicides occur that appear to have been caused by a serial killer's car near Bend, Oregon.
The BAU responds quickly after a serial killer releases a new strain of a deadly anthrax virus in Annapolis that threatens the public and puts a member of the team at risk.
In one of its most difficult cases, the BAU is called to Detroit to help track down a serial killer who forces the team into Canada to catch him.
The BAU continues its search for a serial killer who has forced the team into Canada to catch him. Meanwhile, a team member may have become the target of a killer from the past.