The movie follows the crew of a fishing boat called Niamh Cinn-Oir, which is recently joined by Siobhan, a young scientist of faunal behavioral patterns. While sailing, the boat drives through an exclusion zone, and after seeing strange tendrils in the boat connected to a mysterious underwater organism, a strange infection of an unknown parasite starts spreading through the boat.
The movie was released in April of 2020 in VOD format due to the Coronavirus Disease 2019 Pandemic. Due to it's conflicts related to quarantines, infections and how to deal with it, the movie quickly struck a chord with the general public's anxieties, and received a very positive reception from critics and audiences.
- Above Good and Evil: Siobhan argues this, on the Nature Is Not Nice grounds, in regards to the creature in the parasites. It's not evil, it's simply going along with its reproductive cycle of doing so by infecting whales.
- Big Bad: The parasitic creature lurking just beneath the boat. Its incredibly contagious infection is what puts the crew at risk and sews all of the film's conflict.
- Both Sides Have a Point: Once the crew figures out that they are in the middle of a parasitic infection, Siobhan splits against the rest of the crew on the course of action. Siobhan points out that if even one of them leaves with the parasite inside them, they're likely to infect many others and start an epidemic, starting by their own families; the crew points out that they can't survive in the boat that long, and they could use the medical help. Siobhan, in the end, turns out to be correct.
- However they could have contacted the shore and warned them of the issue and possibly met with proper medical help halfway there. Siobhan's sabotage of the ship not only dooms everyone but keeps the rest of the world from knowing about the threat and it's only a matter of time before another ship gets attacked and there's nothing shown to be preventing the creature from moving closer to land seeking prey either.
- Dwindling Party: It takes a while, but the body count starts racking up in the final stretch of the movie. Johnny is the first one to go, being infected with a grave wound in his hand, and the parasites kill him quickly. Sudi is gravely wounded and his cuts won't close, prompting him to eventually die from them. After an inspection, Gerard is found to have the parasite, and, on his request, Freya kills him. Ciara goes crazy and tries to kill Siobhan, and she shakes her off, but in the process Ciara falls down the stairs and dies. After killing Gerard, Freya has a breakdown and leaves the boat alone, leaving Omid and Siobhan alone and her own fate ambiguous, finally, Siobhan kills herself in order to avoid her own infection to spread.
- Eye Scream: The parasites seem to favor living in the eyes of the people it infects and kills them through it. Johnny dies with his eyes bursting with parasites.
- Final Girl: Sobhan is a smart and strong willed scientist that takes the lead when the crew is infected by a mysterious parasite. Subverted in the end, where she realizes she is infected right when she and Omid are about to get help. She realizes she is done for, but she can still save him, so she jumps into the water and dives towards the bio-luminescent creature, leaving Omid as, ambiguously, the only survivor of the crew.
- Generic Doomsday Villain: The parasitic marine lifeform that threatens the crew isn't fleshed out beyond the threat it poses to the crew and the potential ramifications of its infection being carried to civilization. It's precisely this that makes the creature more alien and frightening.
- A House Divided: Siobhan's insistence in a quarantine separates the crew quickly, especially when Ciara blames her for Johnny and Sudi's deaths. The eventual revelation that Gerard drove them through a forbidden zone and that's the cause of the infection, further divides them.
- Nothing Is Scarier: In the end, we never get any real information about the creature itself. Siobhan can't even properly figure out what it is, with the only information she can guess is that it mistook the boat for a whale, and it is never named. All we get is a glimpse of its bio-luminescent tendrils connecting to something in the bottom of the sea.
- Sea Monster: The creature that infected the crew with parasites is referred to by Siobhan simply as another marine organism, but it certainly has the traits with one, being a dangerous, tentacled and mysterious being from the depths.
- Uncertain Doom: Freya leaves the boat altogether after killing Gerard, but it's unclear whether she is infected, whether she died on the way, whether she got to land safe and sound, etc. It'd be days to get to the shore, so if she was infected, she'd probably die trying to get there.
- Wham Line:Siobhan: Another shoal dead ahead. It's a big one!Gerard: Red?Siobhan: Yeah?Gerard: That shoal is moving pretty fast...