When Aster wakes alone, stranded, on a tropical island, she has no idea what has happened, why she is there, or where to find her younger sister, Poppy. The answers lie in the secretive underwater world surrounding the desert island, populated by the beautiful and the unexpected...

Aster's last memories are blurred. All she can remember is being on a boat with her aunt and other members of the eco-village where she was sent to live after the death of her mother. But Sam, who once met the sisters on a plane, makes links between the mystery of their disappearance and suspicious happenings in his own life. Though Aster can't think clearly, she feels the answers to all of her questions may lie beneath the sea. But nothing can prepare her for the secrets and revelations that she will uncover in her search for her sister. In a stunning dual narrative, the truth unravels with devastating effect -- and the answer lies in the secret underwater world surrounding the desert island. The more Aster searches for Poppy, the more strange things she finds. There is a secret deep in the water. A secret with the potential to change medical history.