Dennis and his faithful hound Gnasher are out to make every day as much fun as possible, but their adventures often lead them into trouble. Dennis is left in charge of looking after the school's pet parrot, Polygon, for the weekend, which he promptly trains to menace Walter with water bombs. When Dennis and co nip home for some dinner and leave Gnasher in charge, Walter sneaks in and sets the parrot free... this doesn't look good for our troublesome twosome! Dennis goes to school with a heavy heart the next day to own up... or will Polygon swoop in to the rescue?
