Free-spirited New York doctor Polly (Kristen Wiig) has never danced to the beat of her biological clock, but when her gay best friend Freddy (played by the film’s writer-director Sebastián Silva) and his partner Mo (Tunde Adebimpe) ask her to be a surrogate for their child she finds she is happy to oblige.

Despite her enthusiasm, the process is far from straightforward, not least because Freddy is something of a man-child himself. A self-obsessed performance artist, his latest video project – the ‘Nasty Baby’ of the title – involves him acting like a newborn, complete with nappies and dummy, a one-note joke that’s reflective of the narcissism which undoubtedly fuels his desire to procreate. Freddy’s low sperm count, however, means that it’s the more down-to-earth Mo who must take responsibility for creating life with Polly, his reluctance influenced by his disapproving family.

This trio are, intentionally and extremely, the definition of urban hipster, and the film holds an unforgiving mirror up to the self-absorbed indulgences, and eventual limitations, of such hard-nosed liberalism. Chilean helmer Silva succeeds in keeping his characters sympathetic and their relationships honest, if unconventional, and his approach is bolstered by some terrific performances. Through their interactions, both amongst themselves and with the world around them, Silva makes a confident return to the issue of class conflict he previously explored in 2009 drama The Maid.

Because, despite Polly, Freddy and Mo’s determination to forge their own path through the brownstones of Brooklyn, an audacious – and genuinely shocking – third-act twist involving belligerent, homophobic neighbour The Bishop (Reg E Cathey) throws a dark shadow over their idealistic values. The film also works as a damning allegory about the supposed democracy of modern America, in which the most progressive of lifestyles can come under serious threat from conservative outside sources. It’s a potent message, given additional resonance in this particular US election year.

Selected release from Fri 8 Apr.