In a remote and solitary fishing boat navigating the turbulent waters of the Atlantic, a reluctant marine biologist named Siobhán joins the crew for a research expedition. What seems like a routine venture turns into a nightmare when a mysterious parasite begins to infect the crew, transforming the journey into a desperate struggle for survival. As paranoia takes hold of the group, they start to question the morality of their decisions and their own sense of humanity.
Siobhán, who initially struggles to connect with her colleagues, is forced to lead amid the chaos. Trapped on the boat, far from the shore and with limited resources, each of them must face not only the external threat of the parasite but also their own internal demons. Tensions rise as disturbing discoveries from the ocean itself start to intertwine with the boat's situation, leading them to question their connection with nature and what it truly means to be human.
With each passing hour, the pressure intensifies, and the bonds that should unite them begin to crumble. The atmosphere becomes increasingly claustrophobic, and the mystery behind the fever of the sea reveals itself as a chilling reflection of humanity's deepest fears. It is a race against time between reason and madness, where the struggle for survival is just the beginning of something much more terrifying.