Diego Arce is a well-known mystery writer who is going through a rough patch. Since the publication of his first novel, which catapulted him to fame, he has failed to achieve similar success. After significant pressure and other literary failures, he gives in to his editor's requests that he should write a new book featuring the character to whom he owes his success: a psychopath nicknamed 'the Monster' who kidnapped young girls in modernist Barcelona. But one night, while Diego and his wife attend a party, someone decides to turn fiction into reality and revive the Monster by kidnapping Ariadna, Diego's seven-year-old daughter. In a dark game, the Monster sets Diego three challenges that he will have to solve live online if he wants to get his daughter back. What will he be capable of in order to save his daughter?