There can hardly be a deeper, darker vale of tears at this year’s Berlin film festival than Season of the Devil, the stylised yet starkly austere, four-hour film in black and white from Filipino director Lav Diaz, about the brutal period of martial law imposed on his country by President Marcos in the 1970s. I have had mixed responses to Diaz’s films recently: I admired the grandeur and mystery of his “Russian adaptations”, that is, his The Woman Who Left (2016), a version of Tolstoy’s story God Sees the Truth, But Waits; and Norte, The End of History (2013), a loose reworking of Dostoyevsky’s Crime and Punishment. Sometimes however, the sheer opacity and impenetrability of his film-making, and of course his natural tendency to let his features run to epic length – and beyond – has been forbidding. In some ways, his work is the cinematic equivalent of open-ended plainsong.

The comparison is not entirely arbitrary. Because the extraordinary thing about Season of the Devil is that it is a bizarre sort of musical. The majority of it is sung through. But there is no chance of an original soundtrack album of Season of the Devil going to iTunes. Because the singing in it is of a bleakly subdued sort. It is all unaccompanied and the melodies are a kind of moaning lullaby-lament, the same for the Marcos militia gangsters as for their oppressed civilian victims. The identical musical style is disconcerting, but conveys the sense that everyone is labouring under the same grim harmonies of evil and despair. This musical conceit put me in mind of Joshua Oppenheimer’s documentary about Indonesia, The Act of Killing (2012). Season of the Devil is shot in a deep-focus monochrome, in a series of scenes each shot from a fixed camera position. This makes for some superbly composed images, particularly the exterior daylight locations. But Diaz has an exasperating habit of shooting indoors in the semi-darkness with a single light source directed straight into the camera. In many ways, Season of the Devil isn’t an easy watch.

The story concerns Hugo (Piolo Pascual), a well-known dissident poet and author whose wife Lorena (Shaina Magdayao) is a doctor; she journeys out on her own to set up a charity clinic in a remote village where Marcos’s ugly goons have already begun their crackdown in response to a growing disorder linked to political murders. The husband and son of a woman called Kwago (Pinky Amador) have been abducted and killed and she is an almost choric figure of keening desolation. The sinister gangsters of tyranny swagger about, and Marcos himself is represented by a very disturbing figure who has Marcos’s face stitched to the back of his head: a nightmare image, like something Dr Hannibal Lecter might have dreamed up. Inevitably, the shock-troops of oppression turn their attention to Lorena, and it is Hugo’s grim destiny to travel to this village himself to discover what has become of her.

Part of the Marcos regime’s approach is to spread bizarre lies and rumours among the rural population: that there is evil and Satanism abroad, and that malign spirits and wicked beasts – obscurely connected with left-wing anarchy – are killing people (when in fact of course it is the Marcos partisans who are carrying out the slayings) and their brutal martial law is needed to suppress the forces of darkness. The widow Kwago is derisively nicknamed the “Owl”, one of the animalistic/communistic figures that they are justified in getting tough with.

Ironically, this poisonous campaign of mystification has a kind of truth. There are indeed evil forces aboard, poisoning the well of society in the Philippines: the Marcos secret police. And Diaz’s film is a gloomy, subdued opera of pain about this season of evil.

Season of the Devil is the work of a real auteur: every millisecond of his film has been rigorously created. There are moments of dreamlike intensity and the despair of the period is genuinely conveyed. Only the strongest devotee of Diaz could however deny the presence of longueurs in this film, and I periodically feel that his austerity and length is sometimes unrewarding. Well, Season of the Devil is a film that has stayed with me, from the deadpan poetry-reading scenes at the beginning to the bone-scraping anguish of Hugo’s horror at the very end. Season of the Devil has a tragic weight.