While his mum recovers from cancer, Joe (and Bingo - the only psychic dog in England) stays with cousin Molly and her dad at the scientific research institute in the countryside. Early one morning, Joe hears a strange wailing sound - like an animal in distress. Molly hears it, too, and they trace it to the disused swimming pool at the back of the institute. However, there are no animals: the scientists are meant to be researching plants. Then Molly and Joe make an amazing discovery: a creature which is part-plant and part-animal. The Planimal can photosynthesise and make its own food. It's a mind-blowing discovery with huge implications for the scientific world. Some people, however, want to use the Planimal for their own selfish ends. Who are they, what do they want, and can Molly and Joe defeat them - and set the Planimal free?