Mistake-prone Alvin, nervous Simon, and music-loving Theodore live comfortably with their adoptive father, Dave Seville, in Los Angeles. Tensions arise when Dave announces a romantic trip to Miami with his new girlfriend, Samantha, leaving the Chipmunks behind. Worse, Samantha brings along her obnoxious, bullying teenage son, Miles. Desperate to maintain their family dynamic, the trio forms an uneasy truce with Miles to sabotage the upcoming Miami vacation, fearing Dave intends to propose marriage and subsequently abandon them.Upon arriving in Florida, the boys discover a ring in Dave's luggage. Driven by sheer panic and a misguided motivation to protect their home, the Chipmunks and Miles hatch a wild scheme to intercept the dinner where the proposal is allegedly scheduled to take place. This desperate endeavor sparks a chaotic cross-country road trip, filled with impulsive detours, wild musical flash mobs, and frantic mishaps that inadvertently put them on the radar of a relentless, humorless federal air marshal named James Suggs, who holds a deep-seated grudge against the singing rodents.Along the adventurous trek, the unlikely group faces numerous dramatic hurdles, including missed flights, wrecked rental cars, and near-misses with Suggs, who relentlessly pursues them across state lines. Despite their initial mutual hatred, Alvin, Simon, Theodore, and Miles are forced to rely on each other’s unique strengths to survive the hazardous journey. Through these high-stakes trials, Miles evolves from a tormentor into a fiercely protective ally, while the Chipmunks realize Samantha genuinely cares about Dave and that their own fears of being replaced were entirely unfounded.Reaching Miami just in the nick of time, the exhausted crew crashes the upscale hotel venue, determined to halt the proposal. However, the emotional climax takes an unexpected turn. Instead of stopping Dave, they accidentally cause an explosive
public spectacle that lands them all in jail. Locked behind bars, the boys finally open up to Dave, expressing their deep-seated abandonment issues and raw
emotional vulnerability. Touched by their profound honesty, Dave realizes the depth of their bond, forgives their reckless behavior, and bails them out.Ultimately, the chaotic ordeal solidifies their broken family into a unified, blended household. Dave decides against proposing that specific night, realizing they need time to grow together naturally. Returning to Los Angeles, the Chipmunks officially welcome Samantha and Miles into their lives with open arms, embracing a joyful future filled with music, mischief, and newfound familial harmony.