Lockhart (Dane DeHaan) was sent to a sanatorium in the Alps to pick up the CEO of the company who was recuperating there. On the way back, Lockhart suffered a car accident and broke his left leg. In desperation, he had to stay in the sanatorium temporarily to recuperate. In the sanatorium, Lockhart met the mysterious girl Hannah (Mia Goth). The weird atmosphere in the sanatorium and the series of scientifically inexplicable events around Lockhart made Lockhart begin to doubt the nature of the sanatorium's operation. The ambiguous relationship between Hannah and the attending doctor Holmes (Jason Isaacs) made Lockhart realize that the incident was not simple. Finally, Lockhart saw through the secret hidden in this sanatorium, and at the same time, his nightmare began.