Kyle Fisher, played by Jon Favreau, is just days away from exchanging vows with his controlling fiancée, Laura, portrayed by Cameron Diaz. Eager to enjoy one last weekend of freedom, Kyle embarks on a bachelor party in Las Vegas with his closest friends: Charles (Leland Orser), Michael (Jeremy Piven), Boyd, played by Christian Slater, and Michael's brother, Adam (Daniel Stern). Their celebratory night quickly spirals out of control in a hotel room filled with booze, drugs, and a stripper named Kobe Tai.
However, chaos ensues as Michael accidentally kills the stripper during a misguided encounter in the bathroom. The fatal moment occurs when he flings her away, leading her to fatally collide with a towel rack. Their night takes a dark turn when a hotel security guard arrives to investigate the ruckus, only to stumble upon the scene. Boyd, taking matters into his own hands, eliminates the guard with a corkscrew, plunging them deeper into a web of deception and panic.
With the clock ticking, Boyd hatches a plan for the group to bury the bodies in the desert. Despite their reluctance, the men comply, but emotional turmoil soon surfaces, taking a toll on their already fraying bonds. Upon returning from Sin City, tension mounts at Kyle and Laura's rehearsal dinner. Adam, consumed by guilt, confronts Michael, resulting in a fierce argument that culminates in tragedy when Adam is killed in a car accident instigated by Michael's reckless behavior.
In the aftermath, Adam whispers a secret to his wife, Lois (Jeanne Tripplehorn), before his untimely demise. As Lois gathers everyone at her home, she senses that her husband's death is shrouded in mystery. The group, particularly Michael, faces the pressure of revealing the truth. Just when the facade is about to unravel, Kyle fabricates a story about Adam's escapades in Vegas, momentarily placating Lois.
However, darkness brews as Boyd's intentions become sinister. An altercation erupts when Lois uncovers Boyd's lethal plan, resulting in a harrowing struggle that hints at another murder. In the subsequent chaos, Boyd concocts a narrative to cover their tracks, hoping to shield the remaining friends from police inquiries. The next day proves disastrous as Kyle and Laura learn they have acquired custody of Adam and Lois' two disabled sons and their pet dog, adding to the overwhelming stress for the couple.
As the wedding approaches, Boyd confronts Kyle regarding Adam's insurance payout. In a fit of rage, Boyd attempts to murder Kyle but is unexpectedly subdued by Laura. During the matrimonial ceremony, Boyd resurfaces with the rings only to meet his end in a sequence of unfortunate events, leaving the wedding to proceed without incident.
As time passes, the aftermath of their actions weighs heavily on the group. Kyle attempts to confess to Laura, but instead of compassion, she demands further murderous deeds to eliminate their burdens. Unsure of his resolve, Kyle prepares to execute her orders in the desert; however, in a surprising twist, they all return, only to face an even greater tragedy when they are involved in a fatal car crash.
Eventually, Laura finds herself buried under the responsibilities of the chaos that has ensued. In a bittersweet ending, Kyle, Charles, and the dog all bear physical disabilities resulting from their reckless actions, while one of Adam's sons is also affected. Laura, now overwhelmed by the life she dreaded, collapses in despair—her cries echoing the consequences of their ill-fated night in Vegas.
