Orphaned as a cub, tame grizzly Boog (Martin Lawrence) lives as Park Ranger Beth's (Debra Messing's) oversized pet in her garage, but the warden wants him returned to the wild at last. Thug hunter Shaw (Gary Sinise) is looking forward to the season opening to shoot a bear, and meanwhile, "accidentally ran over" Elliot (Ashton Kutcher), a skinny, wild mule deer who lost one antler when expelled from the herd. The fast-talking screw-up convinces Boog to cut him loose and invites himself to move in. After a disastrous park opening show, the pair ends up helicopter-lifted to a far part of the park. Elliot promises to lead Boog home if he can move in for good, but that proves an apocalyptic adventure for the whole wildlife after Boog accidentally wrecks the beaver dam, with Shaw on the prowl.