Heart Eyes

For the past few years, a serial killer known as "The Heart Eyes Killer," a.k.a. "H-E-K," has moved to different cities in the United States, killing multiple couples on Valentine's Day. In the present year, The Heart Eyes Killer moves to Seattle and murders two couples, one at a winery and another at a spa. A wedding ring engraved with the initials "J.S." is found at the winery.
Ally McCabe, a pitch designer for a jewelry company who has recently broken up with her boyfriend Collin, is ridiculed for a commercial she wrote involving doomed couples, seen as offensive in light of the recent murders. Ally's boss, Crystal, orders her to work with consulting advertiser Jay Simmons, whom Ally had encountered at a coffee shop earlier. Jay suggests they have dinner that night to gain inspiration, and Ally's encouraging friend Monica helps her pick an outfit.
Ally and Jay meet at the restaurant, but Ally grows hostile as they question each other's views on love. An offended Jay leaves and Ally follows, kissing him as she sees Collin approaching with new girlfriend Sienna. From a distance, The Heart Eyes Killer watches. The two of them reconcile and take a cab to Ally's apartment, where she realizes she forgot her key and Jay helps her break in, cutting his hand in the process. Ally helps tend to Jay's wound upstairs, only for The Heart Eyes Killer to attack them. He kills their cab driver and chases them, knocking Jay out; Ally flees until she is able to summon help. Detectives Zeke Hobbs and Jeanine Shaw arrest Jay for the murders, having found him with the killer's mask and weapon.
At the station, Hobbs and Shaw point out Jay's initials match the ones on the ring found at the winery, and that he was in the same cities at the same time as the killer's previous attacks. Ally waits in the lobby with desk officer Fran and IT technician David; on his way out, David asks Ally on a date, but she declines due to her recent stress. As the power is deactivated, The Heart Eyes Killer appears and kills Fran before moving in against Ally. Shaw confronts The Heart Eyes Killer, who escapes and kills Hobbs. Ally rescues Jay, and they flee to a drive-in movie theater, where they connect while hiding. The Heart Eyes Killer slaughters several movie-goers, causing the duo to decide to confront him. In the scuffle, Ally and Jay fatally wound The Heart Eyes Killer, and they unmask him to reveal an unknown man. They are tended to by an ambulance until Shaw, injured but alive, arrives. She offers Jay a ride, which he accepts.
At home, Ally realizes she fell in love with Jay and goes to find him, but The Heart Eyes Killer calls her to reveal that he is holding Jay at a chapel and will kill him unless she comes alone. Ally arrives, and The Heart Eyes Killer is revealed to be David and Jeanine Shaw, secretly a married couple, while the deceased third killer was their fanboy and lover. They have committed every murder, switching out the costume; in particular, David killed the couple at the winery, losing his wedding ring. Their motivation is a kink for killing together for fun.
They present Ally with the choice of killing herself or Jay, but she shoots Shaw instead, hitting Jay in the process. The two couples fight and Jay stabs David in the eye with his own arrow, resulting in David falling on candles, whose wax immolates him. A shocked and enraged Shaw attempts to kill Ally, but Ally surprises Shaw by stabbing her neck with a metal straw and gains the upper hand, pushing Shaw onto the sword of a statue of Saint Valentine, which stabs her through the neck as it slowly decapitates her. David momentarily springs back to life, but Jay shoots him dead with another arrow, finally ending the Heart Eyes killing spree. One year later, Ally returns to medical school and the couple attends a drive-in movie. Jay asks Ally to move in with him, but she instead proposes and he accepts.
In a mid-credits scene, Ally receives a sinister phone call, which is revealed to be a prank from Monica. As she congratulates the couple, the call is cut off.