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.
When Thea Stilton travels to Ireland to search for a missing agent, she finds that the whole fantasy Land of Erin is being threatened by earthquakes, and soon Will Mystery and the Thea sisters follow to help her find the secret of the fairies.
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 diappearance seems to be threatening the whole land.
The underwater kingdom of Aquamarina is in trouble because the enchanted Music of the Sea has stopped playing--so Thea and the Thea Sisters, together with their friend Will Mystery set out on a dangerous mission to find the Sea Violin which will restore color and life to the Kingdom.
The Seven Roses, magical flowers which bloom forever and which are linked to the health of the Land of Flowers, are dying, and the Thea sisters together with Will Mystery must travel to that land to discover the reason--a journey where every flower seems determined to hinder their passage.
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.
There is a crisis in the Starlight Kingdom, one of the fantasy worlds: its stars, powered by a special kind of stardust, are fading and may soon go out forever, leaving the Kingdom in darkness--so the Thea sisters and Will Mystery set out for Brightstar Castle to discover what is wrong, but first they must overcome the obstacles and challenges that the fairies are placing in their way.
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.