The next day at noon, Eugene receives an invitation to Mme. de Beauséant's much-sought-after ball. His cousin adds that she will be pleased to meet Mme. de Nucingen. Eugène promptly leaves to tell Delphine the good news. The young woman is overjoyed at her first chance to enter this select circle. She tells Eugène that her sister will most likely be there wearing all her jewels to crush the rumor that she has had to sell them in order to pay her lover's debts. That evening, Delphine becomes Eugène's mistress, and the happy young man returns to the boardinghouse for what he confidently thinks will be the last time.
The next day, as Eugène is clearing up his room in preparation for leaving the boardinghouse, he finds Vautrin's I.O.U. and is about to destroy it when he overhears Delphine telling her father that something horrible has happened. Her husband has tied up her fortune in speculations and cannot give it back. He has promised to repay her more than that sum, but he asks for complete control for two years and says they will have to live parsimoniously just to keep up appearances.
Upon hearing this, Goriot goes into a violent rage and says that he will ask to look into all the transactions and see to it that they are transferred to his daughter's name. Delphine tries to calm him and finally tells him about the agreement she had to reach: M. de Nucingen will let her do as she pleases (meaning in her relationship with Eugène) provided she lets him use her money; otherwise, they will go bankrupt. For Delphine, there is no alternative, and she tries to convince her upset father, who finally gives up, saying, however, that he will look into the matter.
They are getting ready to leave when the second daughter, Anastasie, arrives quite upset, announcing that her husband has found out about her settling Maxime de Trailles' bills, the last one for one hundred thousand francs, and about her pawning his family jewels. M. de Restaud told her that he did not want a divorce but that she will have to sign her fortune over to him upon request.
This is too much for Old Goriot, who bursts into a fit of anger and depression: angry at his daughters' husbands, depressed at the miserable life the two girls are leading, and reminiscing about their happy childhood. Anastasie interrupts him only to say that the situation is even worse, for she did not receive quite one hundred thousand francs for the diamonds; twelve thousand are still owed and her lover is facing a lawsuit. She points out that she still loves him, does not want to lose him, and is, in fact, asking her father for that sum.
The poor father tries to explain that he has nothing left, that he has just given up his securities to Delphine. At that point the two sisters flare up, reproaching each other for their conduct and for ruining their father. During this bitter quarrel, Goriot becomes more and more distraught, his grief turning into a sort of delirium, his face showing the signs of an approaching fit, his words becoming more and more incoherent as he threatens to murder his sons-in-law, to rob a bank, to kill himself; but for the girls clinging to him, he would have smashed his head against the wall.
All this time, Eugène has been listening, horrified. Finally he picks up Vautrin's note, alters the figure on it, and makes the 12,000 francs payable to Goriot. He then goes next door and hands the note to Anastasie, telling her that it is the amount he owed Goriot.
Anastasie, realizing that a stranger knows her secrets, becomes furious at her sister, while Goriot almost faints on the bed. Rastignac tells Anastasie to keep the money and that he will keep her secret. The countess takes the note and leaves, coming back promptly, supposedly to see her father, but actually to ask for his endorsement on the note. Meanwhile, Goriot's condition seems to become more critical, and he starts complaining of a violent pressure on his head. When he finally falls asleep, Eugène takes Delphine home but refuses to stay for dinner, for he is worried about Goriot. At the boardinghouse, Bianchon, observing Goriot, quickly perceives the signs of oncoming apoplexy.
That evening at the opera, Eugène tries to conceal his worries, but Delphine, in her enjoyment, promptly dismisses the matter, saying that her father is too strong to be affected by such things; besides, her love is the only thing important to her now. She also tells Eugène that Mme. de Beauséant's lover is actually going to be married, that his cousin does not yet know anything about it, and that it will be quite a blow to her when the Marquis d'Ajuda doesn't appear at her reception.
The opera finished, Eugène and Delphine go to the newly rented apartment, and when the young woman leaves him at two o'clock in the morning, Eugene feels so delighted at having conquered a beautiful society woman and at living in such luxurious quarters that he goes to sleep, forgetting about Old Goriot. Delphine comes back for breakfast at twelve o'clock and it is only at four that they start worrying about the old man and that Eugene decides to go to the boardinghouse to bring him back.
Upon arriving at Mme. Vauquer's, Eugène finds out from Bianchon that Old Goriot has had a relapse and that there is only a faint hope of his recovering. Upon hearing Eugène's voice, Goriot proceeds to tell him of another shock he received from his daughter Anastasie. She came back to ask for more money to pay for her dress, so he had gone out and sold his silver forks, spoons, and buckles, and a year's income on his annuity. The father keeps raving of the joy of giving and insists that he is going back into business. Eugène calms him and as soon as Bianchon comes back, manages to have a bite to eat. Then the two young men attend the sick man through the night, applying leeches and poultices and giving him foot baths.
The next day, Anastasie sends a messenger to pick up the money from her father, and Delphine sends Rastignac a letter in which she bitterly reproaches him for deserting her and tells him how much she wants to go to Mme. de Beauséant's ball. Eugène promptly replies that her father is seriously ill and asks whether she still feels like going to a reception under these circumstances. That evening, Goriot's condition has not improved and the doctor is very dubious about the recovery, so Eugène goes to tell Delphine the sad news, only to find his mistress getting dressed to go to the dance. When Eugène tries to mention her father's illness, she abruptly tells him to get ready for the reception. Eugène leaves quite depressed, torn between pity for the old man, contempt for a society that conditions its members to such heartless actions, and passion for Delphine, which has now grown into love.
When he returns, Delphine is waiting for him and briefly asks about her father. He is extremely ill, says Eugène, and we should go and look after him. After the ball, replies Delphine. Eugène's anger grows, and he proceeds to tell her about Anastasie's selfish actions and the fatal effect it had on the old man. On hearing this, Delphine starts weeping, but her social preconditioning gets the better of her and the knowledge that she will look terrible at the party stops her tears.
At the reception, all the luxury of Paris glitters — the chandeliers, the pretty dresses, the jewels — but in the midst of that brilliance, that gaiety, the hostess, dressed in simple white, is trying to hide her grief. Her lover has finally decided to marry Mlle. de Rochefides. Mme. de Beauséant seems extremely pleased to see Eugène and asks the young man in a very touching voice to do her the favor of going to ask the marquis to return her love letters.
When Eugène comes back, his cousin, for the first time discarding her mask of stoic dignity, starts weeping and announces that she is leaving Paris forever and will bury her sorrow in the solitude of the country. She tells Eugène how much his friendship has meant to her, and as a token, leaves him a glove box for Delphine. She then decides to join her guests, among whom Eugène notices the two sisters, Delphine and Anastasie, the latter with the display of diamonds that cost her father so dearly. The young man is quickly claimed by Delphine and spends the rest of the evening with her.
After the guests have retired at four in the morning, Eugène finds the Duchess de Langeais apologizing to her friend for her bad behavior toward her and urging her to stay in Paris. But Mme. de Beauséant's heart has been crushed and her mind is set. Eugène bids her a last farewell and comes back to the pension on foot. There he meets Bianchon, who tells him that Goriot is past saving. Eugène's reply is, "I am in hell, and I must stay there."
This part concentrates on the two daughters and their destructive effect on their father and on Rastignac.
Delphine and Anastasie, just like Mme. Vauquer in the preceding part, will have to pay their debts to a corrupt and ruthless society. They find themselves lacking the all-powerful instrument necessary for keeping up appearances and dignity — money — and, spoiled as they are, they will again turn to their father.
But this time poor Goriot has hardly anything to give, and his daughters' ingratitude bursts out in a jealous rage. They reproach each other for having obtained more money from their father, they throw their corrupt lives at each other's faces, and they will later refuse to leave a social function to attend him during his illness.
This is psychologically sufficient to explain Goriot's attack. Since the beginning, the old man's love had been his whole life, and the powerful means of asserting his love had been his capability of giving and of being of help. As a result, he had been rewarded by his daughters' thanks, which, he tried to convince himself, were expressions of true love. Now that he feels utterly incapable of giving and helping, he is confronted with his daughters' true natures, with their monstrous egoism and their bitter jealousy, and his life becomes meaningless.
Rastignac is also affected by the daughters' actions. He is appalled by their ingratitude and the intensity of their jealousy, but he is now in love with Delphine and ready to forgive many things. We hear him protest several times, however, and we are touched by his genuine interest in and devotion to Goriot, but he cannot leave Delphine and her social milieu. His state of mind is well expressed in his last remark to Bianchon.
A touching moment is Mme. de Beauséant's farewell to Paris. This truly sympathetic character has been crushed by the ruthless Parisian life. She has tried, but in vain, to reconcile her romantic ideals with a materialistic society. The last ray of sunshine has disappeared from the novel.