Parisian girl Sarah is one of a group of children who has a mysterious auto-immune syndrome that forces them to live in hermetically-sealed capsules, while her parents, scientists Mathieu and Anna, desperately search for a cure. Soon after Mathieu returns from Canada with news of a possible breakthrough. A while later, there is an apparent earthquake, followed by the release of a deadly gas which emerges from the ground and begins to spread through the streets, killing everyone who is caught in it and inhaling the toxic fumes.