Carlos Alberto, geologist, amateur speleologist and known to all as CáBé, is a private investigator, under contract with the Portuguese Ministry of Interior. He decides to take advantage of some time off after several days of extenuating surveillance, to explore a cave at the foot of Serra de Sintra, on the outskirts of Lisbon, unaware this will be the start of an adventure that will take him considerably farther than he had initially planned.​