In the tranquil town of Timberline, 900-pound (407 kg) grizzly bear Boog enjoys a captive, but happy existence and spends his day as the star attraction of the town's nature show with nights living the life of luxury in the garage of park ranger Beth, who raised him since he was a cub. One day, the hunting fanatic Shaw drives into town with the one-antlered deer Elliot strapped to the hood of his truck. Boog frees Elliot at the last minute and against his better judgment, before Shaw can go after him. Boog never expects to see his "buddy" again. Elliot follows Boog home and finds him sleeping in the garage and starts to throw rabbits at the window. He tells him to be "free" from his garage captivity and introduces Boog to a world of sweet temptations outside of the garage that he has unknown. When Boog becomes intoxicated with sugar sweets, events quickly spiral out of control as the two ransack the town's grocery store. Elliot escapes before Boog is caught by a friend of Beth, police officer Gordy. At the nature show, Elliot who is being chased by Shaw, sees Boog who attacks him, causing the whole audience in the show to panic before Boog threatens to hurt Elliot. Shaw attempts to shoot Boog, but Beth sedates them with a tranquilizer gun before he could, thanks to Gordy. Shaw flees before he can arrest him for shooting a gun in the town. The two trouble-makers are released into the Timberline National Forest, only three days before open season starts, but they are set over the falls, where they will be safe.
Since he lacks any outdoor skills, Boog takes Elliot as his hapless guide to get him back home to Timberline to reunite with Beth. But in the woods, they quickly learn that it is every animal for itself. The two run into their share of the forest animals including skunks Maria and Rosie, ducks Serge and Deni, panic-stricken rabbits, the Scottish-accented squirrel, McSquizzy and his rogue gang, Reilly and his beaver construction worker team, a porcupine named Buddy who is in search of a friend and the herd of deer led by Ian and Giselle (who Elliot is in love with) With each adverse encounter, Boog learns a little about self-reliance and Elliot gains self-respect and they start to become friends. Day by day, Elliot attempts to lead Boog out of the forest, but it becomes evident that he has no clue where they are going. After winding up at Reilly's dam, Boog and Elliot are confronted by Shaw, Boog then loses his toy bear, Dinkleman, as the current makes the doll flout out of Boog's paw. They end up in a waterfall, which floods and sends the forest animals down it.
At first everyone blames Boog who accuses Elliot of lying to him about leading him home. Elliot admits he thought that if Boog spent time with him, he would befriend him. Boog leaves to unwittingly finds Shaw's log cabin. Shaw returns and talks to his gun "Loraine" and says he would take back what is his, discovers him (like Goldilocks and the Three Bears), and pursues him to the city road where Boog happens upon the glowing lights of Timberline. Instead of deserting his companions, Boog helps the other animals defend themselves using supplies taken from Bob and Bobbie's (two "scientists" looking for Bigfoot) RV while their pet dachshund Mr. Weenie joins the wilds. The next day, Boog leads a rampage against the hunters, sending them running after McSquizzy blows up their trucks with a propane tank named "Mr. Happy". Shaw returns for a final battle and shoots Elliot in the process, which enrages Boog to tie up Shaw with his own gun. Boog rushes over to Elliot's body but soon finds that Elliot survived the shot, only losing his second antler in the fight. Beth returns to take Boog back home where he will be safe, but instead he stays with his friends and all of the animals in the forest. During the credits, Shaw is seen tarred, feathered and tied on the top of Bobbie and Bob's RV, who mistake him for Bigfoot.
- Astonished & Jawdropping