By Thea Stilton
At the beach by Mouseford Academy, one of the Thea Sisters discovers a mysterious boy with blue skin washed up on the shore. He speaks an unfamiliar language, so the Thea Sisters call Thea Stilton to help figure out how to communicate with him.
She sets the mouselings on an exciting journey across the world to hunt for clues about the boy's origins...and they learn that he is prince of the underwater world of Atlantis! He had always dreamed of exploring the world above, but now he doesn't know how to get home. Even worse, an evil rodent is after him! It's up to the Thea Sisters to help him get home safely.
Hardcover early novel, 320 pages.