Suddenly, an earthquake hits Paris. A deadly fog seeps out of hte earth. Panic spreads across the city. Mathieu and Anna are among the few survivors who find refuge on the rooftops and upper floors of the tallest buildings.

But their daughter Sarah is suffering from immuno-deficiency disease which forbids her to leave the hermetic chamber she lives in - and when hours later, there is still no help from the rescue squads, Anna and Mathieu get worried counting the time left on the batteries that power Sarah's bubble.

How can they replace them before they run out of and leaveher unprotected from the spreading danger? Knowing they can only count of themselves and pressed for time, they have to find a way to make it outside through the fog.