Julien obtains a leave of absence and visits his friend Fouqué, who lives in the mountains surrounding Verrières. Fouqué offers Julien a job in the lumber trade, which promises to be quite lucrative in the coming years, but Julien refuses him. Fouqué's tempting proposition gives Julien a renewed energy and vigor to climb the social ladder just like his hero Napoleon.
When he returns to Verrières, Julien realizes that Mme. de Rênal's constant blushing and new wardrobe mean that she is in love with him. He decides to take their flirtation to its logical conclusion, feeling that it is his duty to become her lover. Like a Napoleonic soldier, he draws up a battle plan, thinking of Mme. de Rênal more as an enemy than a lover. One night he sneaks into her bedroom and convinces Mme. de Rênal to let him stay the night.
Julien's love is still only a form of ambition. Mme. de Rênal becomes his mistress and thus makes him feel like he belongs to a higher social class. But Julien soon reminds himself that, although she loves him, Mme. de Rênal is, militaristically speaking, part of the enemy camp. He overhears M. de Rênal and other Conservatives selecting a new town deputy without any liberal's knowledge and realizes that he cannot trust anyone.
Julien's wavering between wanting success in the Church and success in the army climaxes with the visit of a king at Verrières. Mme. de Rênal secures Julien a position in the honor guard that welcomes the king. However, Julien must quickly change out of his military uniform and into his priestly attire in order to assist M. Chélan with the king's services at the church. Although dressing up like a soldier is a dream come true for Julien, he is also inspired by the Bishop of Agde. The bishop's youth convinces Julien that his path to power lies with the Church.
Fouqué's proposal is a defining moment in Julien's life. Fouqué offers Julien certain prosperity but little societal glory. Julien is convinced that he can achieve both financial success and political glory at a young age just as Napoleon did. Julien's rejection of Fouqué's offer is also a rejection of the bourgeoisie: he believes that true success in French society cannot be bought, it must be won.
Julien is immediately confronted with this alternative road to success when he realizes that Mme. de Rênal is in love with him. With so few ways to achieve glory under the Restoration, Julien sees his military-like seduction of Mme. de Rênal as the only thing left for a soldier to do. Stendhal describes Julien's behavior with bitter irony in this section. Julien really has no idea what he is doing: when Mme. de Rênal asks him if he has a nickname, Julien is unable to respond because that question had not been anticipated in his battle plan. Although Julien is a romantic hero, Stendhal's seventeenth-century influences lead him to also describe Julien as "stupid" and "awkward." But Julien does succeed in becoming Mme. de Rênal's lover, and forgets that it was his tears and not his bravery that compelled Mme. de Rênal to let him spend the night with her. Julien's "victory" makes him think that power can still be attained in French society by following Napoleon's example. Stendhal's reference to the scheming of M. de Rênal and other aristocrats proves that Julien is right to think of the Rênals as his enemy.
However, the king's visit makes Julien reconsider his need to fight battles in order to conquer French society. Wearing the military uniform of an honor guard brings him closer to the glory of Napoleon, but as the day continues he realizes that the Church has become a more powerful institution than the army. This section best illustrates the tension in the title of the novel. Julien must choose between the red uniforms of the army and the black dress of the Church. His indecision is shown at the Verrières church, where his priestly cassock barely covers the army boots he did not have time to change. Yet, when Julien meets the Bishop of Agde, he decides that the Church is where he can become most powerful. The bishop is only eight years older than Julien, and thus about the same age as Napoleon when he became a famous general. Julien understands that the young Napoleons of his day seek power and glory in the Church. Mme. de Rênal realizes this as well, hoping that Julien will become a powerful Church figure with strong ties to the monarchy.