Lamorne Morris' Melvin is the quiet, nerdy classmate at the center of an ill-fated April Fools' Day prank. What begins as a classmate-scaled joke among a tight-knit group of high school friends quickly spirals out of control when Marlin’s football strike drives Melvin into a piece of rebar, leaving him fatally impaled. The group panics, drags Melvin's body into a wooded area, and staging a scene to resemble a random gang attack, they watch the consequences of one careless moment ripple far beyond the prank itself.
Exactly one year later, tragedy continues to stalk the group. DeAnna is stabbed to death by a hooded figure while interning at a hospital, and the killer scrawls "April Fools" on a wall in her blood, a chilling signature that unsettles everyone who remembers Melvin’s death. Hearsay and fear collide as Missy reunites with the others, convinced that DeAnna's murder might be tied to Melvin's, though her worries are dismissed at first. The mystery deepens when Eva Hernandez is also stabbed in a locker room after dance practice by the same hooded assailant, who again leaves the grim message on a wall in blood.
Unaware of Eva's fate, Missy attends the high school Spring Jam, troubled by the surveillance footage of DeAnna's murder that had been left in her room by her detective father. The footage helps Missy place the killer, and she seeks help from Malik after witnessing Diego Mendez and a teacher murdered during the event. A fierce confrontation erupts on the dance floor when Malik confronts the killer, but the assailant escapes after fatally stabbing Malik. As the night unfolds, Missy and the others are rounded up by the authorities, and at the police station she divulges her and her friends' involvement in Melvin's death to her father, Detective Ward.
A police officer escorts Missy home, where she is confronted by the April Fools Killer—Marlin—who has murdered the officer and another officer stationed at his house. Marlin argues that he was the only one truly affected by Melvin's death, lamenting how everyone else seemed to move on while his life unraveled. His fury boils over as he attacks Missy, but she manages to briefly incapacitate him and escape, with a determined Marlin giving chase.
In a tense pursuit through the night, Marlin catches Missy, and she defends herself with a rock, turning his own blade against him. Dazed and bleeding, she stumbles away from Marlin’s body and collapses into the arms of her father, who had gone out to find her after piecing together the April Fools Killer's identity. The film leaves Missy and Detective Ward facing the long road to healing, the truth behind the deadly pranks laid bare, and a family’s fight to put the pieces of a shattered year back together.
