Sea Fever

Siobhan, a PhD student, joins the fishing trawler Niamh Cinn Óir along with Captain Freya, Gerard, Omid, Johnny, Ciara, and Sudi as they depart from the Irish coast. The crew is grieving the loss of their daughter Niamh, which casts a somber mood over the voyage. They set off into the sea, with the normal rhythms of fishing interrupted by tension and purpose.

The Irish Coast Guard warns that the planned destination lies in an exclusion zone and could be dangerous. Despite the warning, the crew prepares to continue, driven by the prospect of a large haul. The seed of conflict is sown as risk overrides caution.

Gerard steers the vessel into the restricted area, driven by the need for a big catch. Freya and the crew are unsettled but unable to stop him. The ship commits to pushing into the zone despite the danger and potential consequences.

In the zone, the trawler collides with an unknown, shoal-like object and suddenly stops. Omid discovers blue-green slime leaking through hull breaches while Gerard initially writes them off as barnacles. The encounter hints at a larger, alien life form lurking below the surface.

With diving gear on board, Siobhan is sent underwater to cut the vessel free from the object. She encounters the bio-luminescent tentacles of a massive organism attached to the hull and begins to understand the true nature of the threat. The moment sets off a chain of escalating events on board.

The crew tries to haul the creature up with a net, but the animal is too heavy to lift. While freeing the net, Johnny's sleeve is caught in machinery and his hand is cut by rope contaminated with slime. The crew realizes the danger is more than a simple fish scare.

Siobhan, Gerard, and Johnny row to a distant ship for help and discover its crew dead, some with eyes removed. Gerard speculates the deaths are due to 'sea fever' and orders them not to tell the others. The eerie evidence confirms the threat is real and not just superstition.

They return to the trawler and haul a large catch of fish, boosting morale on the deck. Siobhan and Johnny flirt, hinting at a budding attraction amid the crisis. Johnny begins showing symptoms of fever, which Siobhan suspects but hesitates to confirm.

Johnny declares he will bathe; Siobhan checks his eyes and spots something moving inside. He soon goes blind and his eyeballs burst, releasing tiny organisms that slither into the ship's water system. Johnny dies as the infestation spreads through the crew's supply.

Omid realizes Sudi is in the shower and tries to turn off the water, but Sudi delays. The larvae bite him, and he dies from the infection. The ship's water has become a breeding ground for the creatures.

Gerard, Siobhan, and Omid inspect the water filtration system and find that the slime larvae have eaten through the filters. The crew understands that the entire ship's water supply is contaminated. They realize immediate action is required to prevent wider infection.

Siobhan tests the slime with UV light but cannot kill the larvae. With Omid's help, she uses an arc welder to briefly sterilize the water supply. She then insists that everyone quarantines on board for 36 hours to avoid cross-infection.

Gerard's infection surfaces in his eyes and Freya privately says goodbye before he kills himself. Ciara dies when she tries to stop Siobhan from warning others. The crew's fragility and mistrust deepen as the outbreak tightens its grip.

Freya escapes the doomed ship by leaving in a rowing boat, while Siobhan and Omid reassess the situation. The last larva has grown larger and bored its way back into the ocean, prompting Siobhan to set the deck on fire to deter the creature. She boards an inflatable raft while Omid, unable to swim, is dragged into the water by tentacles and rescued by Siobhan, who sustains injuries.

Siobhan cuts her wrist on a tentacle, knowing she is infected, and swims toward the bioluminescent monster. Omid watches from the raft as a rescue vessel appears on the horizon. The film ends with the promise of outside help arriving as the lone survivor remains on the raft.