On April 1, 2007, Desiree Cartier [Taylor Cole] hosts a party at her mansion for her actress friend Torrance Caldwell [Scout Taylor-Compton]. Also present are Blaine Cartier [Josh Henderson], Desiree's brother who controls their joint inheritance, Peter Welling [Samuel Child], a U.S. Senate candidate, Barbie Reynolds [Jennifer Siebel Newsom], Peter's fiancée, and their videographer friend Ryan [Joe Egender]. The party also welcomes Milan Hastings [Sabrina Aldridge], Desiree's social nemesis, and Charles Lansford [Joseph McKelheer], the Chihuahua-toting society reporter, setting the stage for a night full of sharp wit, rivalries, and delicate power plays.
As a long string of April Fool's pranks, Desiree suggests Blaine get Milan tipsy on champagne and seduce her in his upstairs bedroom, while Desiree and several others hover by the cracked-open door, prepared to videotape the affair with a camera Desiree borrowed from Ryan. The moment spirals out of control when Milan suffers a seizure and plummets from the balcony to her death, turning a boastful prank into a shocking catastrophe. The group heads to court, and Blaine loses control of the family fortune, which shifts to Desiree, but they are found innocent and Milan's death is ruled a fatal prank, leaving the sense that the truth has been buried beneath a web of lies and ambition.
One year later, Desiree, Blaine, Peter, Barbie, Torrance, and Ryan receive anonymous invitations to meet Milan's grave at noon on April 1, 2008, with the cryptic PS "I have proof." A messenger arrives with a box containing a letter and a laptop computer. The letter claims that one of the six murdered Milan, and if that person does not confess, all of them will be dead by midnight. The laptop contains footage of Charles drowning in his pool, raising the stakes and forcing the group to confront the possibility that their secrets are about to be exposed.
From the cemetery to the pool, the tension intensifies as one supposed victim after another seems to be murdered, only for the bodies to vanish or reappear. Barbie is electrocuted in a beauty pageant dressing room, Peter's campaign truck runs him down in a parking garage, and Ryan's throat is slit in his apartment, while Desiree and Blaine return to the house to find Wilford, the longtime butler, butchered in the kitchen. After a brief separation from her brother, Desiree discovers him tied to a chair, and soon Torrance brandishes a weapon, holding Desiree inches from another chair. In the ensuing confrontation, Torrance fatally shoots Blaine in the chest, and a chastened Desiree finally admits that it was she who spiked Milan's drink—using Blaine as the fall guy to shield herself.
The others reveal that they had been in on the ruse, dressing as cops and staging fake deaths with the help of special effects crew from Torrance's Boogie Nights 2 set to keep Desiree guessing and to force her to confess. To demonstrate the end of the ruse and to prove her guilt, Torrance fires a revolver loaded with blanks—only this time a real cartridge is in the chamber, and the shot blows off the top of Desiree's head. The same inquest-probate judge from the previous year appears to absolve Torrance of guilt for Desiree's death, while confirming Blaine as the sole heir of the family estate. The final scene shows Blaine driving off in Desiree's red Mercedes, a slow, unsettling smirk spreading across his face as the screen fades.
