It's the end of the school year. The long-awaited moment of the holidays is arrive. The little Nicolas, her parents and Grandma take the road towards the sea, and settle in for some time at the Hotel Beau-Rivage.

When a deadly mist engulfs Paris, people find refuge in the upper floors of the buildings. With no information, no electricity and hardly any supplies, Mathieu, Anna and their daughter Sarah try to survive the disaster.