After meeting the head of the performing arts department, Professor Ratyshnikov, the Thea Sisters investigate why the famous ballerina no longer gets along with Headmaster de Mousus.

It's election time at Mouseford Academy and the candidates from the Lizard and Gecko student clubs face some challenges if they want to get elected president.

When a thief strikes during the Venice Carnival, the Thea Sisters investigate hoping to unmask him before the festival ends.

"The Thea Sisters are going to New Zealand! Their new friend Charlotte wants to show them the sights, and introduce them to Didi, a skeleton of a bird that went extinct many years ago. But when they get to the mouseum, Didi has gone missing! Can they find the stolen skeleton before it is too late?"--

While visiting a movie set in Hollywood, the Thea sisters set out in search of a thief who has stolen an important reel of film from the studio.

Attending an adventure camp in Madagascar, the Thea Sisters enjoy learning about the region's exotic plant and animal species before discovering that someone has been stealing endangered animals from the jungle.

Rushing to India to assist their friend Ashvin, the Thea Sisters learn of his efforts to return captive monkeys to their natural jungle environment and that someone has trained the monkeys to become jewel thieves.

The Thea Sisters travel through Mount Everest to enlist the help of the magical creatures they encounter on their journey to the Cloud Castle, where they are investigating why the clouds are disappearing from the Land of Clouds.

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.

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.