The Thea Sisters, who run a top secret research facility receive an urgent call from their pal Will Mystery. Will shares information about a secret mission and informs them about the magical Land of Clouds.

Clouds are disappearing and the mouselets are out to solve the mystery? Amidst the clouds stands an enchanted world of mythical creature and beautiful fairies. Queen Nephele rules the Cloud Kingdom and she is worried about the clouds being stolen. Help is in its way. Where will the investigation and clues take Thea sisters? Majestic Cloud Castle, elves, fairies, unicorns and an incredible journey to Cloud kingdom. Adventure awaits with Thea Stilton: The Cloud Castle book.