1984 -- Suffolk, England.

When 17-year-old Eva goes missing at sea, everyone presumes that she drowned. Her parents' relationship is falling apart, undermined by guilt and grief. But her younger sister, Faith, refuses to consider a life without Eva; she's determined to find her sister and bring her home alive.

Close to the shore looms the shape of an island -- out of bounds, mysterious, and dotted with windowless concrete huts. What nobody knows is that inside one of the huts Eva is being held captive. That she is fighting to survive -- and return home. . .