Josie Byrne's life is spiraling out of control. And just when she thinks it can't get worse, she wakes to an image of herself in the bedroom mirror. Except it's not her at all—the girl in the mirror is blonder and prettier. And her name is Jo.
The two girls are doppelgängers whose universes overlap every twelve hours at 3:59. Fascinated by Jo's perfect world, Josie jumps at the chance to pass through the portal and switch places for a day.
But Jo's world is far from perfect, and the stuff of nightmares lurks around every corner. And when Josie finds herself trapped there, her life becomes more dangerous—and more deadly—than she ever imagined.