Don, played by Robert De Niro, and Ellie, portrayed by Diane Keaton, were once a devoted couple in New England, enjoying twenty years of marriage before they ultimately separated. Together, they raised three children: Lyla, a character played by Katherine Heigl, Jared, represented by Topher Grace, and Alejandro, their adopted son from Colombia, whose role is taken by Ben Barnes.
As Alejandro's wedding day approaches, Ellie revisits Don's house, only to unexpectedly encounter Bebe, played by Susan Sarandon, who has been Don's girlfriend for eight years and was once Ellie’s close friend. The awkward reunion is further complicated when Ellie finds herself startled by Bebe's advances. Meanwhile, the couple prepares for Alejandro's upcoming nuptials with his fiancée, Missy, portrayed by Amanda Seyfried, during a meeting with Father Moinighan, played by Robin Williams. Tensions rise when Alejandro learns that his biological mother, Madonna (Patricia Rae), plans to attend, stirring feelings of turmoil as his family's unconventional status challenges his mother's devout Catholic beliefs.
During a tender moment, Lyla confides in her brother Jared about her struggles with motherhood, revealing her own separation while he grapples with his own virginity, waiting for the right partner. The weight of family expectations really hits Alejandro as he learns that his mother might not accept the reality of his family dynamic, prompting a request for Ellie and Don to act as a couple for the next three days. This leads to Bebe's evident frustration. Once Alejandro's mother arrives with his biological sister, Nuria (Ana Ayora), family interactions further complicate relationships, especially when Nuria shows interest in Jared.
A chaotic dinner ensues, with unexpected roles—like Bebe as their waitress—leading to humorous yet tense situations. As family secrets unearth, drama unfolds with flirtations and unexpected intimacy, forcing Ellie to confront her past with Madonna in a reflective walk through the woods. The wedding day brings more drama when secrets are revealed and tensions escalate, including a confrontation between Don and Bebe, which ends with a punch. Amid the chaos, Missy and Alejandro decide to elope to escape the pressures of the familial expectations.
The wedding reception becomes a hotbed of revelations and reconciliations, with Jared and Nuria engaging in a passionate encounter, while Ellie and Bebe mend their friendship, only for Don to surprise everyone by proposing to Bebe right there and then.
As the events draw to a close, the dynamics within the family evolve significantly; Lyla reconciles with her husband, Andrew, and Alejandro’s mother forgives him when confronted with her own romantic history. In a humorous twist, just before the credits roll, it is revealed that Lyla has named her daughter Jane, adding another layer of chaos to their already vibrant family tree, complete with the admission that both grandmothers are quite eccentric.
