Book Synopsis Keystone follows the journey of a young sea otter named Ollie. When he unexpectedly leaves his beloved marine ecosystem, he never expects anything to happen. But little does Ollie know, he is an incredibly important keystone species, and without him, the ecosystem will crumble. Young readers will learn about basic biology and environmental science as they follow Ollie along on his path to save his home, but they will also learn the value of kindness, respect, and that everyone is important in their own unique way.