In pre-Revolutionary France, Voltaire champions the oppressed commoners and tries to warn King Louis XV (Reginald Owen) about the growing unrest among his subjects.

The writer has a powerful ally in Madame Pompadour (Doris Kenyon), Louis' mistress, but the Count de Sarnac (Alan Mowbray) opposes him for his own ends.

Voltaire invites Calas' daughter and rightful heiress, Nanette (Margaret Lindsay), to shelter in his home.

Meanwhile, Sarnac tries to persuade the King that Voltaire is a traitor, citing his well-known friendship with Frederick the Great and claiming that it is he who is betraying French secrets to the Prussian ruler.

As a result, Madame Pompadour becomes reluctant to aid Voltaire further, until he arranges it so that she can overhear from Sarnac's own lips his ambition to replace her as Louis' paramount adviser.