As midnight strikes on New Year's Eve, Manhattan socialite Alison Hawkins retreats to her home, blissfully unaware of the lurking danger. An unseen predator prowls the shadows, initiating a series of murders that will remain unaddressed for nearly a year. The mounting frustration of the mayor, overwhelmed by the apparent stagnation, leads him to enlist NYPD Commissioner Frank Starkey, who sees no option but to call upon his brother, the former detective Nick Starkey. Nick is famously the only one with the intellect to catch this elusive serial killer, but his return to the force is complicated because his past dismissal left him embroiled in scandal just two years prior.
With a persuasive push from Frank, Nick agrees to rejoin the investigation, but on one condition: he must be allowed to prepare dinner for Frank’s wife, Christine—his ex-girlfriend, whose memory still stirs complicated feelings within him. As they gather around the dinner table, old tensions come to the forefront, particularly surrounding a canceled check that alludes to Frank’s role in the controversy that tarnished Nick’s once-respected position.
After a press conference that announces Nick’s reinstatement, the tension continues between Christine and Nick during their dinner, where brewing emotions threaten to boil over. The following day sees Nick stepping back into duty, where he begins to piece together the intricate threads of this complex case. His first lead guides him to Bernadette, the mayor's daughter and a friend of Alison, who finds refuge in her apartment, terrified and on edge.
As Nick digs deeper, he realizes a disturbing pattern connecting the murders to dates marked by prime numbers, an insight that suggests a method behind the murderer’s madness. Nick's uncanny ability leads him to predict the next murder's timing on the fifth of the month, only to find his theory upended when a woman is strangled a day earlier. Ironically, the murderer meets their demise dramatically, leaping from a window, leaving a perplexing trail of mysteries to untangle.
Despite Frank and the mayor's quick dismissal of the case, declaring it solved, Nick's intuition hints at a nefarious motive—one that could mean this latest murder was merely a diversion, a smokescreen to mislead the investigators. As he persists in his inquiries, the underlying darkness of the city begins to unravel, exposing its dreadful reality.
While Nick and Ed examine the crime scenes on a Manhattan map, they stumble upon a chilling discovery: the locations of the victims' apartments outline the constellation Virgo, hinting at a calculated design. Adding to the strangeness, every room where a murder occurred features a front-facing window, and organizing these windows according to their respective floors resonates with the eleven notes from the chorus of "Calendar Girl." With this revelation, they identify the killer's next likely target.
In a bold move, Nick devises a plan to use Bernadette as bait, giving her a protective neck guard. As they set up outside a supply closet apartment, they watch as the killer expertly picks the lock. When Bernadette brushes against danger, Nick leaps into action. A fierce struggle ensues, culminating in Nick overpowering the assailant and wrapping them in a hallway carpet before handing them over to the police.
At this moment, Christine arrives with news of her breakup with Frank, but Nick is resolute. His feelings have shifted, setting his sights on forging a new connection with Bernadette instead, decisively turning away from the possibility of reconciliation with Christine.
