Movies tend to run with the idea that love is the blissful romantic ideal we should all spend our lives chasing. Its mere mention implies happiness and contentment, brightness and hope. The great German director Rainer Werner Fassbinder made a career out of suggesting the opposite, that love is little more than a torture device which serves to expedite our path to the grave.

Harry Macqueen’s second feature, Supernova, proposes a third way, depicting love as the sum total of life’s mundane drudgery, of prideful acceptance of unwanted purpose, and the retaining of balance when confronted with the bleak reality of human frailty.

Sam (Colin Firth) is a tapped-out concert pianist who is introduced behind the wheel of a hulking camper van which is ambling its way across the English countryside. His navigator is Tusker (Stanley Tucci), a waspish author with a silver tongue whose ironic, passenger-side commentary becomes more wicked as Sam’s irritation escalates.

It is soon established that the pair are a loving couple, heading out on what is hinted as an enforced holiday – a break that neither of them really wants to take, but that nevertheless seems essential in this moment. As Sam stops off to pick up some dinner supplies, he asks and asks again whether Tusker’s going to be okay waiting in the van, and Tusker seems offended by the intimation that he’s a small child who is prone to mischief. When Sam returns, Tusker is missing, along with the family dog. Sam’s sudden dismay is laced with a sense of world-weariness – that this is something he has had to deal with before.

It is then revealed that Tusker is not well, suffering from early-onset dementia. He knows he has reached the point where he can no longer flippantly dismiss the reality of his deterioration, and he’s aware that he needs to make plans before body and mind are irreparably severed. Anyone who, when reviewing Harry Macqueen’s 2014 feature debut, Hinterland, earmarked the writer-director as one to watch, will be pleased to see that their prediction was entirely on the money, as Supernova, while retaining a similar interest in awkward human intimacies, marks a big leap forward in both scope and assuredness.

The necessary groundwork and context, as detailed above, does hint that we’re plunging into another maudlin, “disease of the week” movie, but the film really comes into its own in the second half as the fraught dynamic between the pair switches gear. Macqueen is less interested in depicting Tusker’s slow-fade into mental infirmity than he is looking at how these two men are able to cross-process this bleak situation with the once-sturdy mechanisms of their own relationship.

It might seem disingenuous to say that the film hangs on a single scene, but a late-game dinner table confab is clearly the film’s dramatic and emotional pièce de résistance, a masterclass of dialogue writing and delivery which taps into some extremely difficult assumptions about the paradoxical sting in true love’s tail. It’s a very fine film, one which sees its creative participants firing on all cylinders as well as one which carefully treads a very fine line between melancholic profundity and dismal bleakness.