Bong Joon-ho's latest film is called Mother—a fitting title, since its lead character (embodied by Kim Hye-ja in a shifty, full-blooded performance) not only fulfills the titular role, she's almost entirely defined by it. From the opening scene in which she accidentally cuts her finger while watching her son get hit by a car, to a late sequence in which revelations about her offspring trigger an act of violent aggression, the maternal instinct dictates nearly every action she takes, whether consciously or otherwise.
The relationship between the mother and her son, Do-Jun (Won Bin), is one whose closeness is born of circumstance, the natural protective instinct of a widow for her autistic kid. But the purity of the relationship is troubled by intimations of incest—the pair share a bed and, as local rumors would have it, not just for sleeping—and an incident out of the forgotten past crops up mid-film as further indication of the perverse uses of an overzealous maternity. Bong foregrounds the oddities of the mother-son pairing through his often baroque compositions, one of which finds the woman feeding Do-Jun soup while he urinates on the sidewalk. The director frames the two acts at opposite ends of the 'scope screen, creating an unsettling, distended flow of liquids whose unnaturalness emphasizes the sinister overtones of the film's central relationship.
One day, after drinking at a restaurant, Do-Jun follows a local girl—known for her loose reputation—into a back lane, only to have his advances rebuffed. The next day the girl's found dead, bludgeoned to death with a rock, and Do-Jun's arrested and sent away for the crime on the slimmest of evidence. Faced with doubts about her son's guilt as well as the official indifference of the authorities, the mother takes up the case herself, looking for clues that will exonerate her son.
From here on, the film unfolds as semi-deadpan procedural, its dry tone disturbed only by a few sudden bursts of violence. As the mother proceeds in serio-comic fashion (the latter tendency finding fullest expression in a scene where she attempts to remove a golf club from the residence of two sleeping lovers for use as evidence) she runs up against a gallery of shifty characters, her son's imperfect memory of the fateful night's events and a conflicting web of testimony which muddles the question of what actually happened. But what matters for the mother is that her son claims he's innocent and, proceeding on that maternal faith, she takes decisive action leading to the possibility of a shared round of mother-son culpability.
In the end, the film becomes a meditation on the twin poles of guilt and forgetfulness, a duality that finds its expression in the final scene, where sullen meditation captured through crisp camerawork gives way to a blissful, golden blur. The son missing from the scene, the mother claims the movie for herself. But deprived of her reason for existence, she shucks the rest of her tenuous identity, and as the curtain closes, she merges (literally, given Bong's suddenly diffuse visuals) into the happily obliviousness of the crowd, dancing in the aisles of a pleasure-cruising bus and breaking the Oedipal chain at last.