Martin Moone is eleven and fed up with being the only boy in a family of girls. With three elder sisters, he's desperate for a sidekick to help him fight his corner. When best mate Padraic suggests getting an imaginary friend, he decides to give it a go. His first attempt is Loopy Lou, who loves practical jokes and is a dab hand at balloon-modelling. But Martin soon gets fed up with Lou's clowning around, so selects Sean 'Caution' Murphy instead. Sean is much more up Martin's street - and full of advice about how Martin should negotiate day-to-day life, from dealing with his sisters' pranks to beating the bullying Bonner Boys. But getting rid of Lou is not that easy, and TWO imaginary friends is a recipe for trouble!