This is the story of the life of a blue whale, the largest existing mammals. This isn't based on the observation of an actual whale named Bally; so in that sense it's not a true story. But this is basically a zoology nonfiction book describing what a young whale's life, first with its mother and then on its own. Yet it reads ALMOST like a fictional tale, with elements of anthropomorphism to help make it an engaging book for children. The illustrations, which aren't meant to be scientific illustrations, add to the sense that this is a story about the actual adventures of a young "boy" whale named Bally.