When Bacchu walks across the house, his misshapen bulk casts ominous shadows on the wall, like Quasimodo on the loose.

Bacchu is 15 and mentally challenged. He is shown no mercy in reputed actor Prasad Oak’s directorial debut Kaccha Limbu, which is based on Jaywant Dalvi’s novel Runanubandh. The provocative and beautifully performed movie is filled with taboo ideas, macabre thoughts and vivid images. Moving far away from political correctness but also keeping distance from the outer edge, Oak sets up a mostly absorbing drama about a couple struggling to bring up their only son while simultaneously trying to hold on to what brought them together in the first place. The Marathi movie has been released with English subtitles.

The most shocking idea in Kaccha Limbu is not that Bacchu’s adolescent hormones have started kicking in, and that Bacchu (Manmeet Pem) paws his mother Shaila one night. It is that Shaila (Sonali Kulkarni) and Bacchu’s father Mohan (Ravi Jadhav) are fed up and honest about it. They have mixed feelings towards Bacchu, and they give expression to their conflicting emotions in different ways. Mohan berates his fate and belts Bacchu. Shaila daubs lipstick and seeks friendship and possibly more when her kindly boss Pandit (Sachin Khedekar) takes an interest in her domestic woes.

A love triangle seems to be falling into place, but the real monster under the bed – literally so in some scenes – is the uncontrollable and underdeveloped Bacchu. Mohan handles the night shift at the telegraph office and Shaila works at a pharmaceutical company to ensure that one of them is around to clean up after their son. They worry about money, and save up coins and single notes for the “Bacchu Fund” that they are setting up for their son. When Pandit gives Shaila a cake for her birthday, she beams as though she has been gifted venison.

Kaccha Limbu (2017).

The parents are the ones with special needs, requiring money, therapy and comfort. The movie goes far beyond the stage adaptation Nati-Goti, which Dalvi also wrote, in examining the daily anguish that marks the couple’s lives. Sexual desire is more explicitly stated, and in three scenes, Oak sensitively handles unthinkable realities of the household. Some of the scenes have the flavour of the Greek dysfunctional drama Dogtooth, but Oak calibrates the cruelty to balance shock with empathy.

Some scenes lean towards the grotesque without needing to, and Oak stretches the story for much longer than it is worth. The heart of the movie is the bond between Mohan and Shaila, which is movingly and powerfully depicted by Kulkarni and Jadhav. Kulkarni is especially effective as the harried wife trying to hold on to her feminine side, and Khedekar is good too as the boss who alters the contours of the couple’s relationship with one another.

The genteel poverty of a Mumbai chawl is superbly lensed by Amalendu Chaudhary in vivid black-and-white to heighten the family’s general state of impoverishment. Colour is used only for scenes and objects that depict a happier past – the hope-filled union between Mohan and Shaila, their joy at the birth of their son, the wedding sari and perfume that remind Shaila of her fading feminine side.

The use of tight frames and close-ups in the interiors has a handsome pay-off in the exterior scenes. By following the characters closely and zooming out only in carefully framed shots, Oak and Chaudhary intelligently recreate 1980s Mumbai – fewer people, a slower time – with the minimum of fuss.

The ’80s setting goes some way towards accounting for the overall ignorance and neglect of Bacchu’s condition, though it doesn’t adequately explain Oak’s disinterest in humanising the teenager. Reduced to a pile of grunts and gurgles, Bacchu is a mere footnote in a larger saga of domestic cruelty. He doesn’t even get a proper name that befits his age. His parents treat him like the child they wish he was, and the filmmaker treats him like a spare part when he is actually the motor driving the show.

Majhe Aai Baba, Kaccha Limbu (2017).