In the middle of the night, Pierre (Cervo) slips out, leaving his boyfriend Paul (Igual) asleep. He gets in his car and starts driving out of Paris, apparently without a destination in mind, taking down numbers from toilet stall walls and researching cruising grounds. In the morning Paul has no idea why Pierre left or where he's gone, but decides to use the hook-up app Grindr to triangulate his location. As both continue on their journeys, they interact with a variety of strangers, sometimes helping them, sometimes asking for help.

Reyboud never offers any back-story about Pierre and Paul's relationship, which was apparently a warm one. Nor is there ever any explanation about why Pierre has done a runner. Is it nerves before their marriage? General restlessness? It certainly doesn't matter to the various people they meet, who represent a cross-section of French life: the lonely librarian (Richard), the matter-of-fact thief (Dosch), the rural young gay guy (Cheve), the pontificating drama queen (Montevecchi), and so on. Even with the strangers along the way, the story is uneven. Reyboud inexplicably revisits some of them and ignores others.

In other words, it's not easy for the actors to develop characters with so little information. Instead, the solid cast members centre on personality and flickers of unexplained emotions. Both Cervo and Igual are fascinating as guys we want to understand better, offering telling glimpses into the inner lives of both men. But without context everything feels like it's heading nowhere. At least the journey passes through some intriguing places populated by colourful people.

But since none of these encounters feels like it matters, it's difficult to engage over such an extended running time. The movie just seems to drift without any sense of purpose. Perhaps the vagaries of human connection are Reyboud's point. Or maybe he's just exploring how people connect to each other in unexpected, temporary ways. Or that relationships are difficult, unpredictable and awkward. Or something. Whatever, the lack of build-up leaves the climactic moments feeling rather underwhelming.

Young teen Thor (Einarsson) is frustrated that puberty isn't coming quickly enough for him. Unlike his best friend Christian (Hinriksson) and pals Mangi and Gudjon (Palsson and Sigurbjornsson), Thor has no public hair, something his sisters (Karlsdottir and Ragnarsdottir) remind him constantly. In other words, life for Thor feels like a series of painful insults. Even the cache of fish he caught fails to impress his single mum (Filippusdottir). And there's also a new uneasiness between him and Christian, a mutual attraction that might be more than friendship.

These feelings are expressed through a series of interactions between the characters and the townsfolk. The slightly older local bully Ginger (Erlendsson), probably a victim himself at a younger age, delights in tormenting anyone who displays even a hint of weakness; secrets travel with lightning speed; and things go predictably wrong when Thor and Christian help a local farmer (Malling) then borrow his horses to impress two girls (Valsdottir and Njalsdottir). Which makes Christian's violently homophobic dad (Gunnarsson) even angrier.

Each of these mini-adventures adds layers of interest for the audience, creating a remarkably detailed picture of this small farming community where there isn't much to do beyond roam around the fields smashing up abandoned cars. Each sequence also gives the fine young cast the chance to create powerfully realistic characters who get deep under the skin. What both Thor and Christian are dealing with at home, in town and within themselves is transparently conveyed by Einarsson and Hinriksson.

The audience experiences every perceived slight and self-created humiliation right along with them, so it's almost unnervingly easy to recognise their yearning to fit in. As one character says, "Just stop being weird and everything will be fine." Filmmaker Gudmundsson sometimes over-eggs this message (the ugly fish metaphor is powerful but unnecessary), and the movie would be even stronger with a sharper perspective and a tighter grip on the meandering, sometimes repetitive scenes. But what the film says about the effects of entrenched, even well-meaning homophobia is too important to ignore.

• TOP 10 FILM

Louis (Ulliel) travels home for the first time in 12 years to tell his family that he's dying. And when he meets them, all of the old connections flare up. Chirpy mum Martine (Baye) wants everyone to be happy, while older brother Antoine (Cassel) picks cruelly at everything anyone says and younger sister Suzanne (Seydoux) tries to work out this brother she never really knew. Meanwhile, Antoine's wife Catherine (Cotillard) quietly watches, finding a wordless understanding of what Louis is trying to work up the courage to say.

It's instantly apparent why Louis left these people behind, but also that he can't escape his connection to them. In most scenes he barely says a word, while the others talk about his success as a playwright and their perceptions of his glamorous gay life in the big city. Every conversation explores the dichotomy: closeness and distance at the same time. And each character uses a different defence mechanism to deal with it. The stage origins make it resemble films like Carnage or August, Osage County, but Dolan puts a purely cinematic spin on everything.

Ulliel has the most passive role in this sense, wryly observing his family as an outsider. Which is of course why he has an unexpected link with the sister-in-law he's never met, played with barely suppressed emotion by Cotillard. Baye and Seydoux are both vulnerable and feisty in their roles, challenging Louis while making sure he knows they love him. And Cassel brings the fireworks as the relentlessly aggressive Antoine, whose hotheaded viciousness is clearly a mask.

Sometimes all of this feels a bit tidy, in a stagey sort of way. And it's also rather talky and pointed. But Dolan directs it with such power that it's impossible to look away. Andre Turpin's camerawork, Gabriel Yared's score and Dolan's own editing are skilfully deployed to build the intensity as well as subtle streams of underlying pathos. And as it builds to a crescendo, the film is quite simply breathtaking.

French politician Jules (Duquesne) is collaborating with the Germans to round up Jews and deport them. He may be doing this to protect his wife and son, but he also clearly enjoys the power. When Russian aristocrat Olga (Vysotskaya) is arrested for protecting Jewish children, Jules arranges a "personal" interrogation. But fate intervenes. Meanwhile, young German nobleman Helmut (Clauss) once had a fling with Olga on holiday in Italy. He has risen through the military ranks to become an assistant to Himmler (Sukhorukov), inspecting corruption in deathcamps, which is where he meets Olga again.

Jules, Olga and Helmut tell their stories to camera in SS-style interrogation rooms, intercut with flashbacks. It's clear that all three are dead, and this is an interview about getting into heaven. But the title also refers to the German ideal of creating paradise by cleansing humanity. Helmut has bought into this dream, accepting propaganda that Communists and Jews are to blame for society's woes. In the year of Brexit/Trump, this depiction of bright people accepting official lies is particularly chilling.

Vysotskaya, Clauss and Duquesne deliver wrenchingly emotional performances as people who understand their right and wrong decisions. Indeed, each acts with compassion and cruelty. Standouts in the textured supporting cast are Sukhorukov's colourful Himmler, Diehl as Helmut's sceptical pal Dietrich and Voronkova as Olga's barack-mate Roza. Each character displays raw desperation to survive against all odds as they watch the world fall apart around them. And Konchalovsky catches the audience off-guard in unexpected explosions of emotion.

Shot as uncomfortable realism, the film's black and white, square-framed aesthetic adds distance, as if all of this happened in another world entirely. It's a clever approach that shifts along the way, mainly because Konchalovsky's interest lies understandably in the Russian angle. But in the final scenes he abandons the moral ambiguity, playing God as he decides which of these conflicted people was good and which was innately evil. This kind of undermines his point that each is a victim of a system that failed to protect them from manipulation and lies.