When Paulina, one of the Thea Sisters, finds a strange blue-skinned boy unconscious on the beach, the sisters set out to solve the mystery of who the boy is and where he comes from--and how to return him to his home.

Thea Stilton and her sisters journey to the land of Minwa, a realm linked to the legends of Japan and wrapped in mysteries and enchantments, to discover why the realm's special lotus flowers are disappearing--and why their disappearance seems to be threatening the whole land.

"Thea Stilton and the Thea Sisters are needed to help Aquamarina, the magical land of the ocean! The enchanted Music of the Sea has stopped playing, and no one knows why. If it doesn't return soon, the realm will perish! The mouselets and their friend Will Mystery travel to the underwater world to find the magical music. On their mission, they swim through dangerous waters, encounter strange and fantastical creatures, and even reveal an ancient mystery....

When Will Mystery calls, the Thea Sisters answer the call because there is trouble in one of the fairy kingdoms: a dragon has been turning all the fairies' precious gems into stone, and wrecking havoc throughout the Crystal Kingdom--and it is up to the sisters to find out why the dragon is destroying this Kingdom and stop him before it is too late.

The Thea Sisters are summoned to the Seven Roses Unit by Will Mystery, but when they get there Will is missing; the sisters follow a trail of clues to the Fantasy Kingdoms, and find out that the Mayhem Mirror has been disturbed, and a terrible curse is about to be unleashed on the Fantasy Kingdoms, and it will be up to them to find the eight Harmonies which can break the curse and save the Kingdoms.