Animation. Dennis lives in Beanotown with Mum, Dad, little sister Bea and his pet dog Gnasher. Gnasher is more than a dog to Dennis; he is a kindred spirit. Whatever Dennis does, Gnasher does with him. Together with their friends Curly and Pie Face, Dennis and Gnasher believe the world truly is their oyster and that kids should make the rules. Not everyone agrees, including Mum and Dad. But Dennis and Gnasher are not going to let that stand in the way of their pursuit of fun! The fair comes to Beanotown and Dennis is desperate to go with Curly and Pieface. Unfortunately, Mum needs him to take care of little sister Bea whilst she attends her relaxation class. Dennis will just have to take Bea with him. Arriving at the fairground, the ride operators remember Dennis from the previous year, recalling the chaos he and his friends caused. This year they have put 'safety' measures in place, which prevent Dennis, Curly, Pieface and Bea from having any kind of fun. Angry and upset, Bea threatens to do a poo unless she gets to go on the bouncy castle; Dennis realises that there is only one thing to do. Taking advantage of the operator's tea break, Dennis finds a hose and starts to fill the bouncy castle for Bea. Caught in the act, they flee the scene, leaving the castle rising into the air behind them... Dennis has used helium by mistake. Worse still, Dennis realises Bea has gone missing. Pieface, however, can see exactly where she is; she has climbed aboard the now airborne castle. Horrified by the fact that his baby sister is currently floating above Beanotown in a bouncy castle, Dennis pulls together and executes a daring plan to rescue Bea. Bea is safe, but the bouncy castle is ruined. Dennis has landed himself in trouble again.