Life sucks for 12-year-old Irish American Ava when she is dragged back to Dublin by her mother after her parents' messy divorce. She is bullied at her new school and her only friend is moody teenage neighbour Mal, who has secrets of his own. But when Ava finds a sliver of an emerald and a bundle of old letters in the attic, she is plunged into a historical mystery linking the missing crown jewels of Tsarist Russia to the heart of Ireland's bloody civil war in 1922.