Toriyasu, a fifth-grader, and his younger sister Meeko have been missing their dog Papadoll for a week when two cats carry them off one night to Banipal Witt, a hidden land belonging to cats, where the sun turns people into cats and dogs into monsters. Papadoll was taken there and has grown into a huge monster dog under the command of the wicked Bubulina, whose touch turns any living thing into a balloon. With him at her side, she means to rule all of Banipal Witt. Joined by a group of feline engineers, the children must restore Papadoll and the ballooned citizens before sunrise, or share their dog's fate.