When Mackenzie wakes up with a severed crow's head in her hands, she panics. Only moments earlier she had been fending off masses of birds in a snow-covered forest. In bed, when she blinks, the head disappears. Night after night, Mackenzie’s dreams return her to a memory from before her sister Sabrina’s untimely death: a weekend at the family’s lakefront campsite, long obscured by a fog of guilt. But when the waking world starts closing in, too—a murder of crows stalks her every move around the city, she wakes up from a dream of drowning throwing up water, and gets threatening text messages from someone claiming to be Sabrina—Mackenzie knows this is more than she can handle alone.