Guillermo del Toro (Pan's Labyrinth, Hellboy) presents the story of Julia (Belén Rueda, The Orphanage), a woman suffering from a degenerative sight disease who finds her blind sister Sara hung in her basement. Despite all signs pointing to suicide, Julia decides to investigate what she intuitively feels is a murder case. Julia's sight gradually deteriorates as she uncovers the terrifying truth about Sara's death, and an invisible man with a mysterious link to Sarah begins to stalk her and leave a series of unexplained deaths in his trail.