On a winter night, Mark Schluter’s truck turns over in a near-fatal accident. His sister, Karin, returns reluctantly to their hometown to look after him. But when he finally awakes from his coma, Mark believes that Karin – who looks, acts, and sounds just like his sister – is really an identical impostor.

Shattered by her brother’s behaviour, Karin contacts neuroscientist Dr Gerald Weber. But what Weber discovers in Mark begins to undermine even his own sense of self. Meanwhile, Mark, armed only with a note left by an anonymous witness, attempts to learn what really happened. The truth of that evening will change the lives of all three beyond recognition.