Mother (15)

Where do you go these days if you're looking for real storytelling in cinema? I mean complex plotting, revelations and reversals – everything that makes for rich narrative pleasure. These qualities are thin on the ground, and even when you find a film that spins a compelling yarn – as in current Argentinian thriller The Secret in Their Eyes – you still tend to feel you're watching the equivalent of a good read translated into pictures.

What's truly rare is the sense of drama totally elaborated as cinema, with the storytelling making itself felt in every aspect of a film. But a few film-makers still have the secret, and one is Bong Joon-ho, a South Korean director whose meticulousness and love of confounding the viewer are altogether Hitchcockian. Bong directed the terrific monster movie The Host, about a giant fish-thing on the rampage (I haven't touched herring since) and before that, the labyrinthine Memories of Murder, about the entanglements of an unsolvable crime.

Bong's new feature Mother is almost a perfect film, in the sense that no image, no moment is wasted: everything plays its part in the narrative web that he spins with co-writer Park Eun-kyo.

Mother begins with a knockout opening shot: in a field of long grass, an elderly woman, mournfully starts to dance to a swaying Latin beat. Is she dancing from sorrow, or madness? The subsequent long flashback explains it all. The woman, played by Kim Hye-ja, is a small-town herbalist and acupuncturist who lives with her son Do-joon (Won Bin), a 27-year-old with learning difficulties and problematic short-term memory. When Do-joon is charged with killing a high-school girl, he can't defend himself because he has no idea what happened on the fateful night. Determined to clear him, his mother parleys with the cynical, lazy local police; calls in a contemptuously high-handed lawyer; then sets out to play detective herself.

The plot takes a drastic turn when a clue emerges by chance, and the mother goes in search of a lost piece of evidence that apparently holds the key to everything. But what's exceptional about Mother is that, in this film, pretty much everything holds the key to everything. There are virtually no throwaway touches: it all signifies. The smallest details play a part in elaborating and unravelling the plot, or else speak volumes about the world in which mother and son struggle to survive.

Take the moment early on where she shuffles deferentially around the police station, handing out complimentary goodies; she's an old hand at abasing herself to keep Do-joon out of trouble. A classic "what-just-happened?" thriller, Mother constantly provides little signposts, nudging you to notice things – but as often as not misdirects you about their significance.

At two crucial points, Doon-jo remembers things out of the blue. One instance is a long-lost memory from his own past that suddenly casts his family background in a very different light. The other is the freak retrieval of a hitherto-unconscious memory, like an image that had somehow fallen between frames of the film – and, given the schoolgirl-murder premise, the eerie echo of Twin Peaks is perhaps no coincidence.

With its edge of social satire, Mother has us rooting for its working-class characters against a corrupt world. The South Korean society depicted here is one in which there's seemingly little in the way of just legal process, not even for suspects with evident mental problems. The system of victimisation seems endemic – from playground bullying to the bitterly ironic way that a small-time hood persuades the mother that he is Doon-jo's devoted friend, even while he's extorting money from her.

The film features some terrific characterisations, the vivid dramatis personae including loathsomely thuggish schoolboys, spoilt bourgeois golfers and a deranged grandmother with a penchant for rice liquor. Won Bin is affectingly mercurial as the hapless Doon-jo, despite being saddled with one of those reverse-moptop hairdos that is international screen shorthand for "lovably challenged".

As for lead Kim Hye-ja, she makes one of the most complex, unsettling mothers in cinema. Forever bustling around in torrential rain, this bastion of unconditional love is an image both of the nobility and the abjection of motherhood. As parent and detective, she's a woman with a mission – but also unavoidably flawed as a sleuth.

A monomaniac fury beneath her stooped, uncertain self-deprecation, she's perpetually surprising: she gets into a knock-down fight with the dead girl's angry mourners, then delicately puts on a dab of lipstick, a lovely picture of the madness of keeping up appearances.

Apparently Kim Hye-ja is famous in South Korea for playing dignified matriarchs – which suggests not only inspired casting, but also audacity on Kim's part in taking on a role so delicately poised on the edge of the grotesque. With its quiet visual brilliance and relishably sombre comic sensibility, Mother is poignant, compassionate and ultimately disturbing in its conclusion that perhaps a detective needs to be deluded to get to the truth.

The thriller of the year, hands down, Mother is about as satisfying as narrative cinema gets.