In the opening scene, we find Josh Parker (Jason Bateman](/actor/jason-bateman)), the Chief Technical Officer at Zenotek, in the midst of finalizing his divorce. As he arrives at the office, we are introduced to his coworkers: Mary (Kate McKinnon), the uptight Human Resources Administrator; Meghan (Jamie Chung), who tends to keep her top unbuttoned; Jeremy (Rob Corddry), the office grouch; Alison (Vanessa Bayer), a woman recently single after her husband’s betrayal; and Nate (Karan Soni), who fakes having a girlfriend to avoid unwanted attention.
Josh makes his way to a meeting with Tracy Hughes (Olivia Munn), a colleague who is developing a promising software program. There is palpable chemistry between them, but Josh lacks the courage to act on it. After work, Josh and his friend Clay Vanstone (T.J. Miller), the branch manager, set off for some Christmas shopping. As they pass the iconic Clark Street Bridge, Clay playfully speculates about the speed required to jump it, which signals a foreshadowing of reckless antics to come. They share some lighthearted moments in a department store, culminating in Clay accidentally toppling a Christmas tree in the lobby.
Meanwhile, Alison is conversing with Fred (Randall Park), an awkward accountant, just before the no-nonsense CEO and Clay's sister, Carol (Jennifer Aniston), storms into the office. Known as 'the Dragon Lady', she antagonizes the team by dismissively removing Christmas decorations and announces the company’s declining sales, leading to branch closures. Amidst the tensions, Tracy proposes her software program designed to provide users access to the internet universally. However, Carol crushes the festive spirit by rejecting the idea of a holiday party, branding it a waste of funds and instructing Clay to call it off.
Clay, visibly upset, retreats to vent in his office with Josh and Carol. Their sibling rivalry is evident, with Carol bitter over their father’s decision to pass the company leadership to Clay instead of her. In a surprising turn, Carol offers Josh a lucrative position in New York, promising double the salary, which puts him in a moral dilemma about abandoning Clay.
As the party begins later on, Josh employs the steadfast security guard Carla (Da'Vine Joy Randolph) to keep the festivities under control, while Joel (Sam Richardson) takes on the role of DJ. Meanwhile, Nate, anxious to appear desirable, bribes an escort named Savannah (Abbey Lee) and struggles with his own complicated engagement with her as chaos unfolds in the form of escalating party antics.
As the night progresses, Walter, initially disinterested, unexpectedly begins to bond with Clay and the team. However, just as spirits lift, quirky encounters lead to unexpected complications, including an impromptu performance by Josh and Tracy dressed as oversized snowmen, and scenes that push comedic boundaries as their office camaraderie is tested.
In a dramatic twist, a citywide internet outage occurs after an erratic accident, which places everyone's jobs at risk. Determined to save their positions, Josh, Tracy, and Mary urgently rally together utilizing Tracy's software to restore connections. In an unexpected resolution, amidst reconciliations and realizations, Josh and Tracy finally share a kiss, and Nate and Alison find a budding romance, while Carol and Clay mend their fractured relationship.
As they head to the hospital for a reunion breakfast, they plan to celebrate with drinks, despite the doctor's strict warnings against alcohol for Clay, signaling that the chaotic night has unexpectedly culminated in newfound connections and an endearing holiday spirit.
