A narrator's notebook falls into a Mediterranean grotto, leaving him among local boatmen and visiting sightseers who trade anecdotes about a legendary siren living in the sea. Villagers explain that she cannot sit on blessed rock or breathe the consecrated air, so she remains submerged, visible only to certain people; one diver's sighting transforms him, making him physically altered, burdened with a tragic knowledge of mortality, and withdrawn from ordinary life. Through vivid coastal imagery and conversational recollection, the tale examines the sea's seductive danger, the clash between local belief and tourist curiosity, and the unsettling personal consequences of encountering the supernatural.