After giving birth, Sigrún is suddenly gripped by a terrible sense of dread as soon as her baby is placed in her arms. She is convinced something horrible is going to happen to her son. Years later, when he and a friend from school fall through ice as teenagers and are revived, her worries finally begin to subside. However, they are soon replaced by another, even more disturbing feeling. Sigrún is convinced that when her son was brought back to life, he returned as someone else.

Árný, a school psychologist hesitantly agrees to help the two teenagers, even though she knows full well that she should not come anywhere near this task due to her own past trauma.

Gísli is a rescue diver. A few years ago, he was sent down to retrieve the bodies of passengers from a plane that had crashed into a lake and sunk. The experience has left him with night terrors in which he experiences one of the passengers sitting on top of him or floating above him. He begins to suspect it is the result of his subconscious altering him to something important that he should have noticed while within the submerged plane.

Sigrún, Árný and Gísli desperately seek a solution to their problems, not knowing they are all headed in the exact same direction – into to the deep, cold and unforgiving waters of the lake.