Hildur Knutsdottir's The Night Guest is an eerie and ensnaring story set in contemporary Reykjavík that's sure to keep you awake at night.

Iðunn is in yet another doctor's office. She knows her constant fatigue is a sign that something's not right, but practitioners dismiss her symptoms and blood tests haven't revealed any cause.

When she talks to friends and family about it, the refrain is the same -- have you tried eating better? exercising more? establishing a nighttime routine? She tries to follow their advice, buying everything from vitamins to sleeping pills to a step-counting watch. Nothing helps.

Until one night Iðunn falls asleep with the watch on, and wakes up to find she's walked over 40,000 steps in the night . . .

What is happening when she's asleep? Why is she waking up with increasingly disturbing injuries? And why won't anyone believe her?