Even though his woods are safe from the machines, Jack the squirrel can't go back. The scientists who captured Rat and his sister's mate Jerk, are searching for him-and show up at his human friend Collin's house. To save Jack, Collin and his mother take him to a sanctuary. There, Jack meets Addy and other rescued squirrels, along with Horse and a bunch of barnyard animals. Collin visits and teaches him the last simple machines: the pulley, the lever, and the gear. Jack shares what he learns with Addy, but it's not enough to save him from Hawk-or the scientists. There's one final battle between humans and animals. If Jack wins, he'll have to run away from everything he knows. If he loses, he will never be free.