Two middle-aged, jobless men, Brennan and Dale, have lived comfortable lives, never leaving the safety of their parents' homes. Brennan resides with his divorced, caring mother, Nancy, while Dale has spent his days with his widowed father, Robert. Their worlds collide when Nancy and Robert meet at a medical conference, fall in love, and decide to marry, making Brennan and Dale stepbrothers. The two grown men are forced to live together and share a room, despite instantly taking a dislike to each other. Their initial animosity is marked by petty fights and attempts to irritate one another as they struggle to coexist under the same roof.

Tension escalates as Nancy and Robert expect the men to act like the adults they technically are. They demand that Brennan and Dale find jobs and contribute to the household, hoping that this responsibility will finally make them grow up. As they begin their haphazard journey towards employment and independence, the pair go through a series of comedic but unsuccessful job interviews. Meanwhile, their childlike rivalry continues to heat up and eventually reaches a boiling point that threatens to disrupt the newfound marital bliss of their parents. This ongoing feud ultimately tests the patience of everyone around them, casting doubt on whether these overgrown adolescents can adapt to their new family dynamic and the realities of adult life.