A rosy glow of self-satisfied emotional intelligence emanates from this film about polyamory from Finland. Alma Pöysti (from Kaurismäki’s Fallen Leaves) plays Juulia, a progressive feminist politician married to Christian pastor Matias (Eero Milonoff); they have one child. When Matias, in anguish, admits he is in love with single-mum parishioner Enni (Oona Airola), but still loves Juulia, she is deeply hurt but boldly suggests an open marriage as a solution. Soon she too begins a relationship with queer nurse Miska (Pietu Wikström) who is together with a maths teacher in Sweden.

Having accepted the validity of polyamory, the movie naturally denies itself and us the vulgar sexy thrill of infidelity and guilty secrets. This makes it much more mature and much less exciting. Pöysti is good as Juulia, but Milonoff – so powerful in Ali Abbasi’s sci-fi film Border – is landed with the dull role of a minister with apparently no work to do other than compose infrequent sermons, and whose persistent characteristic is a supercilious pass-agg emphasis on humility and human imperfection. (That adjective in the title needlingly restates this.)

Jealousy within a polyamorous relationship is shown to be a problem but of course they work through it. The other and perhaps more obvious problem for polyamorous people in public life, even in such a liberal country as Finland, is: what happens when the respective political and church authorities find out? How do they work through the consequences of that? Might they be prepared to sacrifice their public prestige for their relationships? Exasperatingly, the film ducks this issue almost entirely, raising it evasively only at the very end. Thomas Vinterberg’s The Commune from 2016 addressed similar themes about collective sexual and emotional experience but packed more of a punch, and was less afraid of nastiness and unhappiness. Well, it’s good to see Pöysti in such a prominent and grownup role.

• Four Little Adults is in UK and Irish cinemas from 7 June.