A heat wave makes New York glow and the zoo's water has to be rationed, so that none of the animals has to suffer from thirst. But then an unknown thief steals the water from the zoo's own cistern and it comes to a state of emergency. To get water as fast as possible and to prevent the animals from dehydrating, Miss Moon creates a magic diviner that will show them the way to the stolen water. When the children find the thief, they are not surprised.