The crew are a superstitious lot and when they spot she's a redhead almost turn back and put her ashore.
Some time into the outward leg they strike something large which they get entangled with and as Siobhán has said she wishes to do a dive they send her down to see what it is.
No good will come of this.
CW: injury detail, body horror, suicide
Neasa Hardiman's infection based horror is mild but claustrophobic. There are some interesting ideas in it but they sort of don't link up very well being just background and background != plot.
Captain Freya (Connie Nielsen) and husband Gerard (Dougray Scott) are mourning a lost child. Johnny (Jack Hickey) has eyes for Siobhán but it never develops. Omid (Ardalan Esmaili) is a Syrian refugee and talented engineer working a low status job, presumably due to prejudice. Sudi (Elie Bouakaze) has a made-up girlfriend in port. Ciara (Olwen Fouéré) has some strong celtic heritage and religious beliefs.
All these things are there and dangling but mostly used only once after being established. We get into the peril at sea stuff and it looks like it will be a monster movie but it mostly backs away from that. When it comes out the crew could be infected by the monster's larvae it seems to be heading for paranoid "who's infected" body horror like The Thing but again backs down.
So we're left with "need to get home, people are getting sick and dying, can't drink the water" and there simply isn't enough tension in this to make it demand your attention.
A slightly disappointing affair 5/10, not actually bad and I'm glad it exists for its unusual setting alone but missing the spark that it looked like it had at the start.