1984, Suffolk. When 17-year-old Eva goes missing at sea, everyone except her younger sister presumes that she drowned. 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 a mysterious island, 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 to return home.