Just a Breath Away

Sarah and a group of children suffer from a mysterious total allergy, living in hermetically sealed capsules while her parents Mathieu and Anna search for a cure. Mathieu returns from Canada with news of a potential breakthrough, offering a glimmer of hope amid the growing crisis. The family braces for what comes next as the situation deteriorates outside their walls.

A deadly gas emerges from the ground and quickly fills the streets with a choking fog. The family finds refuge in the top-floor apartment of their elderly neighbors, Lucien and Colette. Outside, the city trembles as the fog thickens around their block.

Sarah continues to live inside a hermetically sealed bubble powered by a battery-driven filtration system. The apartment fills with fog and the air grows thinner, but her world remains confined to the filtered atmosphere around her. The family strains to keep her alive while the outside danger grows.

By holding his breath, Mathieu breaks into the floor below to seize an oxygen tank from the neighbor's body and gather essential supplies. He discovers that the fog has killed the elder dog but spares the puppy, creating a faint glimmer of hope. On his way back to the apartment, he encounters a group of survivors moving toward Montmartre and receives two additional masks from a soldier.

Upon returning, Mathieu notices the fog creeping higher and threatening to infiltrate their floor. The top-floor refuge already feels the pressure of thinning air, forcing the family to reckon with the possibility of evacuating again. The home becomes a fragile island as the city sinks deeper into mist.

The next day riots erupt around Montmartre as survivors clash and scramble for safety. Mathieu and Anna decide to flee to Charlotte's house in the hills, where Charlotte shares the same syndrome, so Sarah can join her bubble. The family prepares for a perilous journey toward higher ground.

To move Sarah, they travel to a laboratory to obtain a sealed suit. They are separated when Mathieu falls into the Seine during a dog chase, but they manage to reunite at the lab. After retrieving the suit, an explosion damages Mathieu's oxygen tube, forcing them to share Anna's oxygen while seeking shelter.

Despite repairs, Anna's oxygen is still insufficient for both to return safely, so she stays behind with the suit while Mathieu climbs rooftops in a bid to reach safety. They eventually reach an office above the fog, hoping to survive long enough for a rescue or a plan to happen. The tension between dwindling air supplies and the ever-rising fog intensifies.

Mathieu discovers a parking garage with a large stock of supplies and a cop in charge. Realizing the cop won't give up the resources, he is forced to kill the officer to take what he needs and continue the fight for his family. The city around him sinks deeper into chaos and danger.

Anna returns to the apartment just as her own oxygen runs out, and she discovers the suit was damaged in the explosion. With Sarah's battery exhausted, Sarah attempts to dash downstairs, holding her breath, but she collapses before reaching safety. Mathieu returns to find his daughter dead on the stairs.

As the fog rises further and seeps into the apartment, Mathieu decides to salvage a hazmat suit from a crashed car to adapt for Sarah. Lucien and Colette lie on their bed and await death, unable to help, as Mathieu plans a risky last-ditch effort. The choice to save his remaining family drives him forward.

Mathieu retrieves the suit and a scooter, then drives back toward the apartment. He nearly hits a boy walking without a mask and loses consciousness. When he wakes, he finds Sarah approaching through the fog with Noé, her boyfriend who shares the same condition, and who appears immune to the mist.

Mathieu awakens to find himself in Sarah's medical capsule, his role reversed as Sarah now tends to him. The family’s fragile dynamic has been overturned by the disease and the fog, leaving them in a new equilibrium where Sarah becomes the caretaker. The twist hints at a fragile future shaped by those who share the same condition.