Gary Grobowski, played by Vince Vaughn, and Brooke Meyers cross paths at Wrigley Field during an exhilarating Chicago Cubs baseball game. What begins as a delightful romance leads them to purchase a condo together. Gary works diligently as a tour guide in his family's business alongside his brothers, Lupus (Cole Hauser) and Dennis (Vincent D'Onofrio). Meanwhile, Brooke manages an art gallery for the quirky artist Marilyn Dean (Judy Davis).
However, as their relationship deepens, so do the tensions. After a heated argument that leaves them both frustrated, Brooke feels undervalued. She criticizes Gary's lack of maturity and his failure to contribute to their partnership, while Gary, in turn, is exasperated by Brooke's controlling and perfectionist demeanor. This conflict comes to a head when Gary neglects to help her after a dinner party, prompting Brooke to end their relationship.
In her quest for guidance, Brooke consults her friend Addie (Joey Lauren Adams), while Gary seeks solace with his buddy Johnny Ostrofski (Jon Favreau). With neither willing to vacate their shared space, they decide to coexist as roommates, each trying to provoke the other. Gary fills their home with chaos, from a pool table to cluttered leftovers, even hosting a raucous strip poker night with Lupus and other women. In retaliation, Brooke excludes Gary from their "couples only" bowling team and seeks companionship with other men to arouse his jealousy.
As fate would have it, their friend Mark Riggleman (Jason Bateman) prepares to sell their condo, giving them a mere two weeks to vacate. In a final attempt to revive their relationship, Brooke invites Gary to an Old 97's concert, but in a moment of absence, he misses it, shattering her hopes. Soon after, Brooke decides to leave her job to travel across Europe, and one evening when she returns with a date, she discovers a clean condo and a romantic dinner set by Gary. He pours out his feelings, promising to appreciate her more, but her tears reveal a painful truth: she can no longer invest in the relationship, leading to a heartfelt farewell.
It's later clarified that the date she brings home was merely a client interested in her artwork. Gary, reflecting on his actions during a drink with Johnny, comes to grips with the selfishness that stemmed from his guarded nature. Following their separation, Gary steps up his role in his tour business while Brooke travels abroad. Time passes and by chance, their paths cross again on the streets of Chicago. Amid some polite small talk, they part ways with a lingering glance back at each other, both sharing a knowing smile that hints at unresolved feelings.
