The staff on an exploratory oil-rig are about to wind things up with no success, despite the pleas of tomboy engineer Hae Jun (Ha) to keep trying. However, her uncle Jeong Man (Ahn) shows up and convinces the captain they should persevere. Work continues, until one of the crew is found dead, and suspicions turn to her colleague, who had recently had his affections spurned. The true culprit turns out to be not even human, but a monstrous creature, on which Jeong has been working, hoping to use it as an alternative fuel source, since its body burns better than crude oil. The crew, with no way to get off the rig, have to try and fend off the monster, which whittles away at their numbers, in an apparently unstoppable fashion.
When it gets going, this is a lot of fun, helped by an impressive creature design, with tentacles and a gaping mouth, which looks exactly as if it had crawled up from the ocean floor. Credit also to the makers for not hiding it in the shadows: they are understandably proud of the creation, and want to show it off (the movie was originally in 3D). Ha makes for a spunky 'final girl', whizzing round the rig on her motorcycle, and throwing everything at the beast to try and stop it. The film's main problem is obvious: an over-extended opening act, that takes far too long to get to the stuff that we want to see. Instead, we get failed attempts at comic mugging, with poor chemistry, and characters that we are given little or no reason to care about. Maybe it's a cultural thing?
However, if the viewer shows some perseverance, they'll be repaid with an entertaining monster-romp. For my money, this was more fun the The Host, the other Korean flick which is the most obvious point of comparison. In some ways, they're mirror-images of each other; while that ground to a halt as it went on, Sector 7 improves the longer it continues. The final battle is up there with Aliens in terms of confrontational goodness. I'd have give you extremely long odds against that being the case, as the alleged "humour" based on a character's swollen lip flowed like milk during the early stages.