This simple horror film takes the age-old fear of the sea serpent, modernizes it, and takes it to new heights.
It starts with an unlikely heroine, nerdy graduate student Siobhan, who loves studying oceanography in virtual forms, and has to be pushed to get on a boat and examine it in real life. She finds herself on a small fishing boat, ill at ease with the boisterous crew, who start by exclaiming over the bad luck she, as a redhead, will bring to the voyage. Other seafaring myths and legends are of interest, including one, told to Siobhan by the boat's co-owner, Freya, which becomes relevant to the story. Some of the footage of undersea life not only further the story, but are remarkably beautiful.
Siobhan does her best to fit in, and does make a connection with one or two of the crew members. Things take a sinister turn when the ship is impeded by a creature completely unfamiliar to either Siobhan or the crew. The more they investigate, the more dangerous the animal becomes. Suspense builds as the sea creature's intentions and abilities are gradually revealed, Siobhan tries to understand the creature's nature and possible weaknesses, and the crew works frantically to escape or summon help. The director has the sense to keep the monster mysterious as long as possible, adding to the tension.
It's a well made, well acted, slow-burning horror story.