This slow-moving drama sneaks up on the viewer. After minutes tick by watching sweet old couple Yaojun and Liyun shuffle along, share snacks and ride the bus, one is more likely to burst into a flood of tears than feel bored.

Over its luxurious three-hour run time, this story packs in threads about forced abortions, labour-camp stints for listening to decadent Western pop, attempted suicide and extramarital liaisons. Everything the characters deal with is the result of the child-shaped hole left in the lives of Yaojun and Liyun.

If it all sounds like prime-time soap opera material, that is because it is. But celebrated Chinese film-maker Wang Xiaoshuai, maker of social realist dramas like the prize-winning Beijing Bicycle (2001), Shanghai Dreams (2005) and 11 Flowers (2011, also starring Wang Jingchun), never lapses into mawkishness.

The director knows the value of indirectness and the long pay-off. The scene of the child's death, for instance, is filmed from afar. All that is visible are human shapes running in panic, with the occasional heart-rending sob heard from a distance. Sorrow, shame and guilt are borne with tight-lipped stoicism, making their release explosively cathartic.

The story is a history of the couple and, like all histories, it looks backwards. In a series of flashbacks going back to the 1980s, the pair are shown to be ordinary factory workers. In their lifetimes, they have been moved from city to farm and back again in the name of the Cultural Revolution.

In the 1980s, they are too poor to afford the fine levied on those who break the one-child policy, so they make their lone son their life's work. Later, China will move to a market economy, at one stroke doing away with the iron rice bowl Yaojun and Liyun slaved to secure at their factory.

Yaojun and Liyun come alive as real people, rather than as symbols, despite film-maker Wang's long interest in making sure that his characters are blown around by the winds of political change. He could not have more eloquent actors than Wang and Yong, who play the couple first as young parents then as elderly figures, hanging on to the memory of a lost child in a country that has forgotten them.

• So Long, My Son is part of the Asian Film Archive's New Releases programme. It is screening at the Oldham Theatre, 1 Canning Rise, from Saturday to Oct 28 at various times. Tickets at $10 from solongmyson.peatix.com