With just six months until their wedding, Greg Focker and his fiancée Pam Byrnes make the bold decision to introduce their families. They journey to Oyster Bay, New York, to pick up Pam's parents: her retired CIA operative father, Jack Byrnes, her mother Dina, and her young nephew, Jack "Little Jack" Banks. From there, Jack takes everyone on a road trip in his new RV to Miami to meet Greg's unique family.
Upon arrival, they are welcomed by Greg's free-spirited parents, Bernie Focker, a former lawyer turned stay-at-home dad, and Roz, a sex therapist specializing in the elderly. While Dina strikes a bond with the Fockers, tensions rise between Jack and Bernie due to their vastly different backgrounds and personalities.
A comedic chase ensues between the family dog, Moses, and the kitten Jinx, resulting in Jinx flushing Moses down the RV toilet, only for Bernie to heroically intervene and save the day by destroying the toilet. Later on, a game of touch football takes a turn when Bernie accidentally injures Jack's back.
In a twist of events, Pam reveals to Greg that she is pregnant, and they agree to keep this news under wraps until after their wedding. Meanwhile, Bernie inadvertently reveals to the guests that Greg had a romantic encounter with the Fockers' former housekeeper, Isabel Villalobos, fifteen years ago. This revelation catches Jack's attention, particularly when he meets Isabel's son, Jorge, who shares a striking resemblance to Greg and showcases his handy skills by fixing the RV toilet.
As the plot develops, Greg finds himself in a predicament when he is left alone to care for Little Jack, who has been raised under the strict Ferber method. Ignoring Jack's explicit directives, Greg's attempts to calm the baby backfire comically, teaching him the inappropriate word "asshole." Little Jack soon discovers the joys of television and rum, throwing the families into further chaos.
Suspicion mounts as Jack resorts to spying on Greg, submitting both Greg's and Jorge's hair samples for a DNA test. In a wild turn of events, Jack invites Jorge to the engagement party, hoping to confront Greg over his parental status. When Greg denies any knowledge of Jorge, Jack loses his composure and administers a truth serum, leading Greg to uncontrollably announce Pam's pregnancy and his supposed fatherhood of Jorge during a toast, right before he passes out.
The morning after, when Pam confronts Greg about Jorge, he reassures her that he had no clue about their acquaintance. Surprisingly, Pam stands by him, willing to work through the issues. However, Jack, feeling betrayed, demands that Pam and Dina leave with him, only for Dina to reveal Jack's wrongdoing in drugging Greg. The atmosphere turns against Jack, who is hurt to discover that everyone had already known about Pam's pregnancy, a revelation overshadowed by his lack of trust.
In their pursuit of Jack, Greg and Bernie face a hiccup when Officer Vern LeFlore tasers them for speeding, resulting in their arrest. Meanwhile, Jack receives the shocking DNA results—revealing Jorge's true father is a baseball player who also resembles Greg. As Jack turns back, he witnesses Greg and Bernie being apprehended, and in his attempt to defend them, he too falls victim to Officer LeFlore's tasering.
Thankfully, Judge Ira, a client of Roz’s, bails them out. Before their release, Greg takes a moment to urge Jack and Bernie to mend their differences, prompting an unexpected moment of vulnerability when Jack apologizes for his errors and opens up about his past CIA career.
In a heartwarming conclusion, Greg and Pam exchange vows that weekend with Pam's former fiancé, Kevin, officiating their interfaith ceremony. As new family dynamics unfold, Jack reviews footage caught on hidden cameras, discovering the Fockers' antics—much to his dismay.
