In the arid landscape of Arizona, two lifelong pals, Bud "Squirrel" Macintosh and Doyle "Stubs" Johnson, are suddenly left adrift when their environmentally conscious girlfriends, Jen and Monique, decide to part ways with them due to their childish antics. This pivotal moment propels Bud and Doyle on a journey of self-discovery that leads them to the Bio-Dome, a state-of-the-art research facility where the ambitious scientist, Dr. Noah Faulkner, is gearing up to seal his team inside for an unprecedented year-long experiment. Mistakenly lured by the prospect of luxurious amenities, Bud and Doyle inadvertently lock themselves inside as well, much to the dismay of the scientists.
As the project unfolds, a sense of unexpected harmony develops as Bud and Doyle navigate their unfamiliar environment. Yet, as their reckless behavior escalates, chaos and disarray ensue at the facility. The scientists, exasperated by the duo's antics, plead with Dr. Faulkner to take action, but he remains resolute, fearing that removing the friends could lead to disastrous outcomes.
As their adventures continue, Bud and Doyle stumble upon a hidden stash of junk food and an experimental laughing gas that ignites their mischievous spirit. This revelation prompts them to indulge in a series of wild escapades, leading to their eventual exile to the deserted section of the dome. The duo soon learns that their former girlfriends are attending an environmental gala, inspiring them to throw a party of their own. However, this ill-conceived plan backfires, further distorting the experiment's tranquility and alienating Bud and Doyle from their loved ones.
In a moment of clarity, as the scientists prepare to exit the dome, Bud and Doyle intervene, advocating for everyone to join forces to revive the Bio-Dome. In a frantic act of desperation, Doyle swallows the key, igniting a chain of events that unites the group in their shared goal. As their efforts to restore the dome continue, Bud and Doyle forge unexpected friendships with the scientists, capturing the attention of Monique and Jen along the way. On the other hand, Dr. Faulkner becomes increasingly unhinged as he concocts a diabolical scheme involving coconuts rigged with explosives.
As Earth Day approaches, Bud, Doyle, and their allies manage to rejuvenate the Bio-Dome just in time. However, on the brink of revealing their work to the world, the duo's unannounced visit to Dr. Faulkner uncovers his intention to showcase pyrotechnics at the reopening ceremony. Oblivious to the fact that these festivities include dangerous explosives, Bud and Doyle, caught in this explosive situation, must navigate their way out before disaster strikes. The impending explosion heightens the stakes, forcing Bud and Doyle into a frantic race against time to thwart Dr. Faulkner’s nefarious plans.
As the final moments of the experiment dawn, Bud, Doyle, and their newfound friends prepare for their exit. Yet, Dr. Faulkner has one last trick up his sleeve, launching one final coconut bomb at their departure, transforming their exit into pandemonium. With a farewell to their scientific comrades, Bud, Doyle, Jen, and Monique venture into the unknown, only to have a pressing bathroom emergency lead them towards an enigmatic nuclear power plant. Meanwhile, Dr. Faulkner, having snatched back the key that had hindered him, makes a quiet escape through a concealed desert door, igniting a pursuit with law enforcement close behind.
