Why does Lucien become upset and leave?

Chapter please?

If your question pertains to Chapter 54, Albert encourages Lucien to create gossip that would cause Mrs. Danglars to lose money..... to teach her a lesson. Lucien is embarrassed by the suggestion and leaves.

"Yes. Your position as secretary to the minister renders your authority great on the subject of political news; you never open your mouth but the stockbrokers immediately stenograph your words. Cause her to lose a hundred thousand francs, and that would teach her prudence."
"I do not understand," stammered Lucien.
"It is very clear, notwithstanding," replied the young man, with an artlessness wholly free from affectation; "tell her some fine morning an unheard-of piece of intelligence -- some telegraphic despatch, of which you alone are in possession; for instance, that Henri IV. was seen yesterday at Gabrielle's. That would boom the market; she will buy heavily, and she will certainly lose when Beauchamp announces the following day, in his gazette, `The report circulated by some usually well-informed persons that the king was seen yesterday at Gabrielle's house, is totally without foundation. We can positively assert that his majesty did not quit the Pont-Neuf.'" Lucien half smiled. Monte Cristo, although apparently indifferent, had not lost one word of this conversation, and his penetrating eye had even read a hidden secret in the embarrassed manner of the secretary. This embarrassment had completely escaped Albert, but it caused Lucien to shorten his visit; he was evidently ill at ease.