Two apes are hunted in the jungle and taken to a big city, where they are kept in a zoo and forced to perform monthly for a local circus. Many years pass, and the two apes, now aging, decide to break out and take their revenge on the kind-hearted plumber and his girlfriend who were hired by the circus to mind the apes. This sends the plumber and his brother through construction sites and through the sewers as the apes cause havoc, but soon, the two groups are forced into a truce when an even deadlier threat emerges from the city's underbelly.
