While visiting their grandfather’s beach house in Maine, Addie receives a mysterious treasure box once owned by her grandmother.  In it is a moonstone ring and a mysterious poem. The poem leads Addie and her cousins to nearby Moonstone Cave where, together they enter a secret and magical garden and embark on an adventure of a lifetime.  Alone the way, they meet wonderful friends like Gemma, who reminds them all of a younger version of there grandmother; Jumani, a large white wolf; and Jadira, a strange and smelly creature whom they grow to love.  During the adventure, they learn the most important lesson of all – they must work together if they want to escape the dangers ahead of them and find their way back home.