On demand: "Vaathi"

The foursquare Tamil drama Vaathi goes some distance around the houses to set up a plot that's not a million miles removed from 1995's Dangerous Minds. In the present day, a trio of slacking students start clearing out a shuttered video store, and - behind a row of dodgy DVDs - uncover a stash of VHS tapes. Recorded on the tapes are lessons given by a star educator of the 1990s, a period when teachers in India were being lured away from public schools to fill lucrative openings in government-subsidised private academies. This hero teacher, further inquiry reveals, is one Balamurugan, and he's played by Dhanush of Karnan fame; with his fresh face and sensible haircut, he barely looks long out of sixth form himself. Bala specialises in the teaching of maths and physics, but what with this being a massy entertainer, he's officially introduced laying waste to a mob of hulking volleyball players who've swindled his charges out of their allowances; later, he will see them off for a second time in a makeshift school playground, making a physicist's use of the resident swing set. His true heroism, however - the heroism that wound up enshrined on those VHSes, and now finds itself doubly enshrined in a 21st century streaming option - is revealed after he takes up a new teaching position in a rural backwater, where those families who have the money send their offspring to private schools, and those who don't prefer to send their kids into menial labour. Here, Bala has to fight to fill an otherwise empty classroom, and the film sets out its case for the importance of education as something that cannot - and shouldn't - have a price tag attached to it.

This it does via a combination of familiar to-sir-with-love scenarios and local variations. Of course Bala outwits the scheming, sunglasses-sporting superintendent who's sent our boy out this way to fail. Of course he gets a problem student back on track. And of course he wins the heart of willowy biology-teaching colleague Meenakshi (Samyuktha Menon), although he does so by teaching two classes simultaneously, erasing the caste system by teaching half a lesson to one group, half a lesson to the other and forcing everybody to interact. This alertness to social structures is recognisably - and distinctively - South Indian. According to Vaathi, education in Nineties Tamil Nadu really was a gangster's paradise, run almost like a protection racket in which only those who paid got to play. In this context, Bala presents as a revolutionary, preaching learning for learning's sake; the convoluted framing is there to enshrine him in turn as a legend as enduring as any god or freedom fighter. (Those VHS tapes are as stone tablets.) It sort of works, but chiefly because - as in Karnan - Dhanush never overplays the saintliness. (He can't: after being cast out of the community, Bala opens a new study centre in a rundown porno cinema.) Instead, the star breezes through the film with characteristic casualness, looking as though he'd just shuffled onto set two minutes before the cameras rolled wearing clothes from his own wardrobe. Simplicity does look good on him: even in the action sequences, he falls back on a no-frills fighting style, or redeploys whatever's to hand (a stick, a rock, a volleyball net) to see off his pursuers. He's such a low-key star - so distinct from the brawny poseurs of Bollywood - that he can even turn a technical limitation like the flatness of his line delivery into a virtue in projects like this. A determinedly ordinary hero, Bala is constitutionally unable to grandstand - but Dhanush can make the rolling-up of sleeves seem like its own form of mission statement and, at the last, he turns the nondescript leavetaking "okay sir, thank you sir" into a colossal fuck-you. Pacily assembled by Venky Atluri, it arrives with its own Coolio-style banger in "One Life" (lyrics: Dhanush), the catchiest rap/country crossover since "Old Town Road".

Vaathi is now streaming on Netflix.