A woman named Abigail meets a tragic fate in Scotland when a delivery boy, disguised as a harmless courier, ruthlessly kills her. The investigation into her death reveals a gruesome scene, with her head, arms, and legs arranged in a cross-like formation while her torso is notably absent. This bizarre pattern eerily resembles a series of murders that terrorized Chicago over five years earlier. To assist in the case, the police enlist the expertise of Detective Dan Lawson, who had worked on the previous killings alongside his now-retired partner, Walker Bravo.
Upon arriving in Scotland, Lawson collaborates with investigating officer Glen Boyd and chief of police Laura Kessler. Boyd is grappling with personal turmoil related to the loss of his son, which complicates his ability to focus solely on the case. During their investigation, Lawson and Boyd discuss the nature of the crimes, suggesting that the primary difference from the original Chicago murders may lie in a religious motivation, hinting at the possibility of hate crimes.
As the two detectives grow closer, Boyd reveals the strain his family has endured following their child's death, detailing how his wife, Marie, has become distant, resulting in a betrayal during their grief. Lawson shares his own past pain involving a victim named Sarah from the Chicago murders, and they bond over their shared heartaches while vowing to track down the killer targeting innocent lives in Scotland.
As their investigation deepens, Lawson returns to consult with Bravo to gain further insight into the case. Meanwhile, Boyd suspects that Abigail's neighbor may have some connection to the crime. However, they hit a dead end when the neighbor proves uninvolved, making the path to justice seem daunting.
Their efforts take a dark turn when another victim, a woman named Grace Hall, turns up dead, similarly staged. Boyd learns of Grace's ex-boyfriend, Colin McGregor, and works to question him, but Colin's evasiveness under the presence of his lawyer complicates matters. Tensions heighten as Boyd discovers Colin's previous involvement with a local cult, only to find additional clues leading him back to another suspicious sighting near the crime scene.
As the investigation escalates, Boyd successfully apprehends Colin; however, upon returning home, he experiences a devastating discovery when he finds Marie murdered in a fashion hauntingly similar to the other victims. Stricken with loss, Boyd vows to catch her killer, suspecting Colin's connection to the crime. When Boyd threatens Colin during interrogation, his actions begin to unravel the thin threads of the investigation, leaving Lawson and Boyd in disarray.
A complex game of cat and mouse ensues as Colin meets a brutal end at the hands of the real killer, who proves to be a far more formidable foe. Upon discovering Colin's history and a chilling resemblance to previous murder methods, Lawson realizes they are not yet finished. As further investigation reveals Lawson's knowledge of Colin's crimes and a possible connection outlines a more profound truth, the shocking reality of the case unfolds.
Through layers of deception, it is ultimately revealed that Lawson himself is behind the murders, driven by revenge and the dark corridors of his own past intertwined with Boyd's family. In a calculated move, Lawson eliminates those who remind him of his own unforgotten pain. The final confrontation leaves Boyd grappling with enormous loss and frustration as he desperately pursues Lawson, who stays one step ahead.
The film concludes on an unsettling note, leaving Boyd's pursuit of justice incomplete and Lawson eluding capture, enjoying a serene moment in nature, suggesting a chilling justifying of his horrific actions. With the case now in the hands of Interpol, Boyd's anguish echoes as the unresolved ache of his wife's murder continues to haunt him, marking the end of a harrowing journey filled with betrayal and darkness.
