In the vibrant autumn of Oakton City, set in October 1959, a notorious duo of squirrels, Surly (Liam Neeson) and his trusty mute sidekick Buddy, navigate life as outcasts in Liberty Park due to their reputation for thievery. As the community of urban animals rallies around Raccoon and his loyal confidant Cardinal, they face a dire situation: the relentless winter threatens their food supply. Amidst this turmoil, Andie (Maya Rudolph), a compassionate squirrel, and Grayson (Brendan Fraser), driven by ambition, compete fiercely over the contents of Lucky and Fingers' nut cart— which is, unbeknownst to them, a front for the criminal machinations of Percy "King" Dimpleweed.
In a twist of fate, Surly and Buddy’s antics inadvertently cause a propane tank explosion in the park, ignited when Fingers' pet pug, Precious, takes a bite out of a wire. This chaotic incident sends the nut supply into disarray, resulting in Surly’s banishment from the park, but not without igniting a spark of audacity in him.
Fate leads Surly and Buddy to Maury's Nut Shop, a murky establishment entwined in criminal dealings where Lucky, Fingers, and the cunning King, along with his thuggish henchman Knuckles, scheme to pilfer the bank's riches, substituting it with an array of nuts. Lana, King's unsuspecting girlfriend, remains in the dark about his nefarious plot, convinced that her partner has turned over a new leaf post-incarceration.
Separate from Surly's adventure, Andie and Grayson are tasked by Raccoon to forage for food for their struggling community. However, they become sidetracked by a street rat, which leads them to find Fingers' abandoned dog whistle. Andie, seizing this opportunity, aims to leverage the whistle against Surly, who, after an accidental encounter with Precious, becomes a part of her conflicted trajectory. As whispers of this plan circulate amongst the community, Raccoon begrudgingly sends Mole and the Bruisers alongside Andie.
With suspicions brewing thanks to a heart-to-heart with Mole, Surly trails the group, yet after his warnings are dismissed by Andie, he storms off. His run-in with Grayson leads to his capture by King; however, a real twist unfolds when Lana—having realized that King remained the same as ever—steps in just in time to liberate Surly.
In a breathtaking chase involving the street rats under Raccoon’s command, Surly and Grayson cleverly intercept the criminal crew’s getaway vehicle. While Cardinal momentarily finds himself outmatched, Mole’s defecting from Raccoon's allegiance paves the way for a revelation that unravels Raccoon’s hold over the park animals. However, King and Knuckles plot a disastrous detonation with dynamite from an abandoned truck to breach a police barricade, which goes horribly wrong when the authorities intercept their plans, leading to a catastrophic explosion that sends everyone spiraling into the river.
In the aftermath, Surly clings to a log as the torrent threatens to sweep him away along with Raccoon, who seeks vengeance. Just when it seems all hope is lost, the community arrives to rescue Surly. In a moment of ultimate sacrifice, he allows himself to be dragged along with Raccoon over a waterfall, thus redefining his legacy among the park inhabitants.
As the tumult settles, King and his criminal gang face the consequences of their actions, while Lana severs ties with him. Andie and Buddy, deep in mourning for Surly, are surprised when Precious discovers his unexpected survival. Encouraged by her, Buddy visits Surly, who awakens and greets him with undeniable affection. Surly’s heroism begins to spread, yet he chooses not to boast about it, instead showing a profound willingness to collaborate with his fellow animals.
In their new adventures through the city, Surly and Buddy let Grayson bask in the glory of their exploits while the shadows linger with King and Knuckles scheming their revenge. In a surprising post-credits scene, the enigmatic PSY appears, joyfully busting out some moves to "Gangnam Style." Meanwhile, Raccoon and Cardinal are seen, very much alive, plotting their next move from a precarious buoy amidst circling sharks, setting the stage for their audacious return.
