Sea Fever

As the Niamh Cinn Óir sets sail, PhD student Siobhan (name not specified) joins Captain Freya and her crew of six on their fishing trawler. The group includes Gerard, Freya's husband and skipper, who is still reeling from the loss of his daughter Niamh; Omid Hamilton Accie, the ship's engineer; Johnny; Ciara; and Sudi Hamilton Accie. Despite receiving an alert from the Irish Coast Guard about an exclusion zone in their planned destination, Gerard takes a calculated risk to enter the area, driven by the need for a substantial catch to keep the vessel afloat.

Their journey takes an unexpected turn when the boat encounters an unknown object submerged in the water, causing them to stop abruptly. Engineer Omid's discovery of strange breaches in the hull reveals a peculiar blue-green slime oozing out, which Gerard mistakenly attributes to barnacles. As Siobhan prepares to dive with her research gear, Gerard dispatches her to cut away the entangled vessel, unaware of the extraordinary sight that awaits her beneath the surface.

As she explores the dark waters, Siobhan finds herself face-to-face with an enormous, bio-luminescent creature's tentacles attached to the boat. Returning to the surface, she shares this astonishing revelation with Gerard, who hypothesizes it might be a newly discovered giant squid. The crew attempts to capture the behemoth using their net, but its sheer size proves too great. During the commotion, Johnny's sleeve becomes entangled in the machinery, resulting in a gruesome hand injury contaminated by the mysterious slime.

Siobhan and Gerard join Johnny on a desperate bid to seek help from another vessel looming on the horizon. Upon arriving at the ship, they stumble upon the macabre sight of lifeless bodies in the cabin, many appearing to have succumbed to an otherworldly force, while one individual seems to have had his eyes brutally removed. With a sense of foreboding, Gerard orders Siobhan and Johnny not to reveal this disturbing discovery to the others.

Upon their return to the Niamh Cinn Óir, they find that the creature has inexplicably released its grip on the vessel. The crew's spirits lift with the successful haul of fish, but Siobhan and Johnny share a moment of mutual attraction as they tend to the injured hand. As tensions simmer beneath the surface, Johnny develops a fever, which Siobhan suspects is caused by an infection, but he refuses to allow his hand to be examined, leaving the fate of their burgeoning romance uncertain.

As the revelry on board subsides, Johnny announces his intention to take a midnight swim, only to be halted by Ciara and Siobhan. Sensing something amiss, Siobhan shines a torch on Johnny's eyes, revealing an unsettling sight: tiny organisms wriggling beneath the surface. As he rinses his face, Johnny's vision abruptly falters, and his eyeballs rupture, releasing the malevolent entities into the ship's water system. He succumbs to the infection, and Omid frantically attempts to intervene as Sudi showers away, oblivious to the impending danger.

Meanwhile, the trio of Gerard, Siobhan, and Omid inspects the vessel's filtration system and discovers it has been compromised by the aquatic larvae, which have devoured all the filters. This realization dawns on Siobhan, who deduces that these creatures are the precursors to the gargantuan sea monster whose eggs permeate the slime. Gerard takes the helm, steering the ship towards the shore.

In a desperate bid to contain the crisis, Siobhan conducts experiments on a slime sample, employing UV light and subsequently electrifying the trawler with Omid's assistance using the arc welder. This sterilization effort seemingly eradicates the waterborne threat. However, she insists that they must all self-quarantine aboard for at least 36 hours, the duration it took Johnny's infection to manifest. Her argument is met with resistance from the others, who argue Sudi requires medical attention and that hospitalization would be necessary if any of them are infected.

Tragically, Sudi meets his demise due to the infection. Siobhan subsequently disables the boat by entangling its propeller, rendering it inoperable.

As the survivors conduct a visual examination of each other's eyes for parasites, Siobhan, Omid, Freya, and Ciara appear to be uninfected. However, when Freya discovers larvae in Gerard's eyes, the couple shares an emotional farewell before Gerard takes his own life.

Siobhan becomes increasingly suspicious that Ciara is infected, prompting her to ascend the ladder to warn the others. When Ciara attempts to intervene, Siobhan forcefully knocks her off the ladder, ultimately condemning Ciara to a fatal outcome.

As Freya rows away from shore, Siobhan and Omid's pleas to reconsider fall on deaf ears. Meanwhile, their frantic search of the water tank yields a devastating discovery: the last remaining larva has miraculously survived and grown stronger, its insatiable appetite having taken a toll on the boat's hull. As the vessel begins to take on water at an alarming rate, Siobhan and Omid resort to drastic measures, dousing the deck with white spirit in a desperate bid to create a beacon of hope. In the chaos that ensues, Siobhan commandeers an inflatable raft, while Omid, his swimming skills woefully lacking, succumbs to gravity and tumbles into the depths. Though Siobhan manages to rescue him from the clutches of the lurking tentacles, her own wrist becomes entangled in a gruesome display of bioluminescent fury. With a fatalistic acceptance, she declares herself infected and plunges back into the abyss, drawn inexorably towards the creature's radiant glow. As Omid watches on alone, his raft drifting precariously close to salvation, the faint outlines of rescue vessels appear on the horizon.