It is virtually impossible not to use words like “restrained” to describe Robin Williams’s mild-mannered performance in The World’s Greatest Dad, a superb jet black indie comedy from writer/director Bobcat Goldthwait.

The reason is obvious: for decades Williams has been the bouncy flibbertigibbet, the elastic-faced crazy-eyed man flogging his own distinct brand of manic cheerfulness. Over the last decade or so the amphetamine glaze has worn off, partly because Williams has mellowed with age but mostly because of very deliberate creative decisions. Buoyed by Good Will Hunting, for which he won an Oscar in 1998, Williams got deeper and darker in the years since, his glares particularly icy, mean and resonant in thrillers Insomnia (2002) and One Hour Photo (2002).

His range widens still in The World’s Greatest Dad, but not in a way that can be conveniently described as simply “dark” or “dramatic.” Williams’s performance is an odd fusion of emotions, not unlike the film itself, and he fits like a glove with Goldthwait’s quirky directorial style. The World’s Greatest Dad is by turn sad, hilarious, quirky and grim, and a dark shining gem of a film.

Williams plays high school teacher, father and aspiring writer Lance Clayton, a pleasant but forgettable person, the kind of tea and scones fella who mixes in with the scenery no matter where he is, so long as it’s not a rave or a brothel. Lance is a capable but presumably unspectacular writer, a father subservient to his son Kyle (Daryl Sabara) and a man easily and regularly short-changed in life.

Kyle is a rude and ungrateful brat. He’s clearly struggling through the meaty part of adolescence, confused, horny, I-hate-everything and finding himself, but his personality is brutal enough to solicit only little if any audience empathy.

Something dramatic happens to Kyle around the end of act one. Instead of facing the music, Lance creates a white lie. The film is about what happens when he sticks to it, how it spirals out of control and the mixed blessings he accrues because of it. The mild-mannered earnest-hearted dag finally gets his run in the sun, but – harks the obvious question – at what price?

Goldthwait’s screenplay is genuinely unpredictable. It is acted almost perfectly, the cast underlining their acting with wink wink sassiness – a bunch of sharp and funny, acerbic and witty performances, but collectively warm and humane underneath.

To say much about the story risks spoiling some of its surprises. One thing you ought to know, especially if you’re a Queen or David Bowie fan, is that The World’s Greatest Dad – and yeah, if you haven’t deduced by now, the title is tongue in cheek – has one of (if not the) most memorable uses of Under Pressure ever committed to celluloid. It’s also one of the best, most refreshingly perverse black comedies in yonks.