In this 'deliciously creepy' (TV Insider) psychological thriller, Helena visits her troubled twin sister, Siri, at a secure retreat in the Italian Alps. But when she wakes up the next day, Siri has stolen her identity and fled, leaving Helena trapped inside a clinic where nothing is what it seems.

The critically acclaimed drama returns for six more riveting episodes. In this season, DC Kate Fleming and DS Steve Arnott of AC-12 investigate the conduct of Sergeant Danny Waldron of the Armed Response Unit.