Spring has sprung and Verne (voiced by Garry Shandling) and his woodland friends awaken from their long winter's nap to discover that a tall green “thing” has mysteriously cropped up right through the middle of their home. Enter RJ (Bruce Willis), an opportunistic raccoon, who explains that the world beyond the hedge is the “gateway to the good life” where peculiar creatures called humans live to eat, rather than eat to live.

Suspicious and even a little jealous of RJ, the ever-cautious turtle, Verne wants to keep his blended family safely on their side of the hedge. But, proving the adage that one man's garbage is another man's – or rather, animal's – treasure, the manipulative RJ tries to convince the woodland band that there is little to fear and everything to gain from their over-indulgent neighbours. Eventually, RJ and Verne form an unlikely friendship as they learn to co-exist with – and even exploit – this strange new world called suburbia.

Rounding out the voice cast are Steve Carrel as a hyperactive squirrel named Hammy; William Shatner as Ozzie, a possum who excels at playing dead with a melodramatic flair; Avril Lavigne as Ozzie's daughter, Heather; Catherine O'Hara and Eugene Levy, who are paired as the porcupine couple, Penny and Lou, with a brood of little porcupine mouths to feed; Wanda Sykes as a sassy skunk named Stella; Nick Nolte as a bear named Vincent and Omid Djalili as a spoiled housecat named Tiger. On the human side, Allison Janney plays Gladys, the president of the local homeowners' association, who isn't about to see her neighbourhood overrun by wildlife and Thomas Haden Chruch as “The Verminator”, whom Gladys hires to rid the area of our woodland heroes.