Meet Siri Bergman.

She lives alone, an hour outside of Stockholm where she practises as a psychotherapist, her nearest neighbour far away.

She is terrified of the dark.

Siri tells herself that she has moved on since her husband died in a diving accident. But when she goes to bed at night, she leaves all the lights on, unable to shake the feeling that someone is watching her.

What if she has good reason to be afraid?

One night she wakes to find that the house is pitch black, and the torch by her bedside has vanished. Later the body of one of her young patients is found floating in the water nearby. Thrown headlong into a tense murder investigation, everything Siri believed is called into question.

Can she trust anyone?