Miss Mary-Kate Martin and her mother are off on an adventure to the enchanting Greek island of Galinios. An ancient mosaic has been unearthed and Professor Martin must investigate, leaving Mary-Kate to explore the island and bask in the sunshine.
But soon her relaxing holiday turns into a monster-sized mystery, when a message arrives asking for help.

Could the local legend of the Two-Headed Hydra be more than just a story? And what could have made this serene sea creature so angry?
Miss Mary-Kate Martin might be anxious, but she’s not scared of monsters! With the help of her new friend Nikos, she is determined to find answers.