You need to stay for the entire 90 minutes of French-Canadian director Francois Delisle’s “Chorus,” and not get up and leave midway through.

Although you will want to.

“Chorus,” the tale of parents dealing with unimaginable grief, made all the worse because it has been long deferred, is extraordinarily hard to watch at times. Several patrons at the press screening I was at Saturday did in fact head for the exits halfway through.

But you need to see it through, to see the arc that Delisle has constructed, and the way it bends, not sharply but slightly, back out of darkness towards light. It’s a really good film, but one that’s unflinching in the way it sees loss as an inevitable part of the human condition.

“Time does not heal,” Irene (Fanny Mallette) says flatly in a voiceover early in the film. Ten years earlier, her eight-year-old son Hugo disappeared without a trace from a neighborhood park. She’s been in a state of emotional paralysis ever since, grieving and not grieving, knowing and not knowing. Singing in the local church choir gives her some comfort, but the sight of a friend’s newborn baby sends her racing out of the church, choking for air.

Her husband Christophe (Sebastian Ricard) was unable to take the loss, and turned away from his wife, running off to Mexico, where he claims the ocean calms him a little.

Now, a pedophile in prison has confessed to murdering Hugo, and tells police where his remains can be found. Christophe comes home, and the long-delayed acceptance of loss can finally begin. As wrenching as many of the scenes are, that the couple are finally turning towards each other for comfort gives “Chorus” a glimmer of hope. The film moves towards a conclusion that, if not quite healing, at least points towards that direction.

Both Ricard and Mallette give potent, unguarded performances, especially Mallette — there are scenes where she is perfectly. still, and you can see the tremors of emotional pain start flaring up in her until she collapses from the sheer force of her grief. Genevieve Bujold also makes a small but memorable appearance as her mother.

Delisle shot “Chorus” in lustrous black-and-white, and the film reminded me of Pavil Pawilowski’s “Ida” in the beautiful compositions of the stark grey shots. There’s one absolutely devastating scene where husband and wife walk up the aisle of their son’s memorial service, a grotesque echo of a wedding ceremony.

The sound design is also powerful — aside from the church choir, there is no score for “Chorus” until late in the film, when music suddenly suffuses the film (including an unlikely appearance by the rock band Suuns), like a dam finally bursting.

It’s a long, dark road to that catharsis, but it’s worth the journey to get there. I won’t easily forget “Chorus” – it’s currents run too deep.