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.

A shocked Hel learns that her sister has reportedly died in a car crash. A fellow inmate tells Hel that she a psychiatrist embedded as a patient, and that she believes her story. They decide to talk to Fisher, her long-time friend and colleague.

Hel's fellow inmate is brutally tasered by Fisher when she confronts him. Another doctor discovers Hel is telling the truth, but is driven off the road and killed by another member of staff. As her options are rapidly running out, and Hel has nothing to lose, she decides to accept a 'kamikaze' plan to escape. But nothing ever seems to go to plan in Himmelstal…

Hel desperately tries to persuade staff that she is not a psychopath, but no one believes her claims. Dr Kowalska discovers Dr Fisher's true unsettling mission behind the sanctuary.

Helena (Hel) Brant visits her estranged twin sister Siri at a luxurious alpine sanatorium, Himmelstal. Much to Hel's horror, she soon realizes the sanctuary is an escape-proof psychiatric hospital and Siri has swapped places with her, leaving her trapped.