In 1957, in the small town of Moorehigh, something sinister is happening as patients of Dr. Evan Rendell start vanishing without a trace. The shocking truth emerges as the townsfolk uncover that a father-son duo has been chillingly extracting the hearts of these patients, driven by the desperate hope of resurrecting Dr. Rendell's deceased wife. This nefarious scheme leads to a confrontation with the police, resulting in Dr. Rendell's fatal shooting. In the aftermath, his son, Evan Jr., mysteriously disappears.
Fast forward to 1992, a whopping thirty-five years later, the adult Evan Jr., now infamous as "Dr. Giggles" due to his unsettling laugh and obsession with following in his father's dark footsteps, breaks free from a mental institution, leaving a trail of corpses in his wake. Meanwhile, Jennifer Campbell, a 19-year-old burdened by family troubles and a serious heart condition, is trying to enjoy her summer break along with her boyfriend Max Anderson and their group of friends. As tensions rise, Dr. Giggles returns to his childhood residence, digging through his father's records to compile a list of victims, leading him to stalk and eliminate several locals, including Jennifer's friends.
After a particularly tumultuous party, in a fit of rebellion against her heart monitor, Jennifer discards it into a fish tank. This action prompts her father to search for her, just as Dr. Giggles arrives and fatally attacks her girlfriend, who is set to become her stepmother. Upon her return to the party, Jennifer is heartbroken to see Max kissing another girl. Overcome with emotions, she flees into a funhouse. Noticing that Jennifer shares the same heart condition as his mother, Dr. Giggles pursues her, killing Max's new crush in the process. Fortunately, Jennifer narrowly escapes and is rescued by Officers Magruder and Reitz, who take her to safety.
Officer Magruder recounts the harrowing tale of Evan Jr.'s escape to Officer Reitz. He reveals that while on duty at the morgue, he witnessed Evan Jr. gruesomely emerging from his mother's body, a shocking revelation that sends him into shock. As Magruder lies disoriented, all evidence of the horrific event has vanished upon regaining consciousness.
Dr. Giggles soon tracks down Jennifer's father, leading to a brutal confrontation. Officer Magruder arrives only to find her father gravely injured and in a pool of blood. Magruder recognizes Evan Jr. and manages to shoot him before succumbing to his wounds. Reitz arrives too late to save his partner and find Jennifer's father alive but critically hurt.
Back at his lair, Dr. Giggles performs self-surgery to remove the bullet from his body, capturing Jennifer and plotting to "fix" her heart using organs he harvested from her friends. As the climax unfolds, Reitz and Max make a heroic entrance. While Reitz keeps Dr. Giggles occupied, Max and Jennifer make their escape. Tragically, Dr. Giggles kills Reitz, yet his plans meet a chaotic end when his father's house detonates around him.
In the hospital, Jennifer learns that the atrocities she faced have badly harmed her heart, necessitating urgent surgery. Just as she prepares for the procedure, Dr. Giggles resurfaces, slashing through hospital staff in a bloody rampage. In a tense moment, Jennifer traps Dr. Giggles in a janitor's closet and ultimately puts an end to his reign of terror with his own surgical tools. In a chilling final gesture, Dr. Giggles breaks the fourth wall, turning to the camera and weakly uttering, "> Is...there a...doctor in the house?" before collapsing lifelessly.
As she recuperates in the hospital, Jennifer is greeted by both Max and her father, serving as a reminder of the chaos they overcame.
