This has to be one of the, if not the, best diving thrillers ever made. Right up there with Open Water—with far higher production values.
I’m not a diver myself, but I’ve watched enough episodes of Dive Talk on YouTube to consider myself an armchair expert…and honestly, the diving in this seemed highly realistic, including the plot points involving safety stops (although they fudged this a little bit) and potential CO2 poisoning. Buddy-breathing seemed well-executed, and even some tenets of cave-diving (frog-kicking and laying safety lines) were observed. (And the actors did their own diving, up to eight hours a day during the three weeks of production.)
Some of the objections noted by other reviewers are perhaps too hasty. I think both characters are strong and resourceful, although of course the character who’s doing the saving has to find her ability through the course of the movie. (Otherwise, no movie.)
Also, I thought the trunk wouldn’t open because she had broken in rather than using the key. (Meaning, prevented by the security system.) Maybe the storytelling could have been clearer there.
Definitely worth checking out if you have an interest in diving, and if you’re looking for a movie with strong female leads. Don’t expect deep characterization, but unless that’s a dealbreaker, you should enjoy this.