You m0natt0m3re@!#! killed my sister and niece, see what I do to you! ... and so started a bloody onslaught.
The plot is logical, as if written by Georg Wilhelm Friedrich Hegel: thesis, antithesis and synthesis, which becomes the new thesis facing a new antithesis until it is resolved in a new synthesis, und so weiter.
The crescendo seems (seems, SEEMS) to be the killing of poor TaeGu, who turns out have been duped into partaking in the carnage.
Then the girl (Jeon YoBin, the FL in "Vincenzo" for those watching the series) shows up. She enters and locks the door ...
The movie's Ulyssa "... sprang on to the broad pavement ... shed the arrows on to the ground ... 'Dogs, did you think that I should not come back ... and now you shall die.'" (Please see the scene in Franco Rossi's Odyssey).

PS I wish the movie had ended just going to a black screen without hearing the shot, leaving the audience ponder whether the bullet or the cancer caused the black out.