Set in the volatile Paris summer of 1938, "The Age of Reason" follows two days in the life of Mathieu Delarue, a philosophy teacher, and his circle in the cafes and bars of Montparnasse. Mathieu has so far managed to contain sex and personal freedom in conveniently separate compartments. But now he is in trouble, urgently trying to raise 4,000 francs to procure a safe abortion for his mistress, Marcelle. Beyond all this, filtering an uneasy light on his predicament, rises the distant threat of the coming of the Second World War.