Making peace with the past and friends for a lifetime. Elly is sent by her father to stay with her Aunt Dina on Sunday Island for the whole summer. With no friends, Elly is bored. So when she receives a mysterious invitation for a midnight meeting, she sneaks out of the house, only to stumble into a bemused girl called Sierra, who is just as lost as Elly. A helpful little dog leads them into an overgrown maze ...where a grinning girl called Tash meets them. 'I thought a midnight feast would be a great start to our summer on Mystery Island!' The three girls have a lot of fun together, swimming, eating ice creams and exploring the island. By chance, the girls discover that their pasts are linked. But an old mystery involving buried treasure threatens their friendship. Will the girls be able to solve the mystery and remain friends?