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 Thea sisters continue the search for the seven ancient treasures, using the clues found in Aurora Beatrix Lane's travel diary to find a fabulous emerald which once belonged to Cleopatra--a quest that leads them from Moscow, to the Sahara, and finally Bolivia.

On summer vacation in Scotland, the Thea sisters are intrigued by a tapestry that is really a treasure map supposedly leading to a hidden alabaster garden where an ancient treasure is buried, and the story of Aurora Beatrix Lane, an adventurous explorer mouse--and when the tapestry is stolen they set out to find the treasure using the explorer's diary as a guide.