Persephone the grateful

"After meeting a water naiad named Minthe in the gloomy Underworld, Persephone is grateful for the happy life she leads. Minthe has to guard the stinky river Cocytus, with no friends around her. When the students of Mount Olympus Academy are challenged to a geo-dashing competition all over the Earth, Persephone wants to win! but it turns out Minthe is definitely a little green with envy over Persephone and her friends. And when the challenge takes th eteam to the Underworld, Minthe shows her true colors and causes big trouble for the team! Can Persephone figure out how to save her friends and how to be a friend to Minthe?"--Provided by publisher.