A few days later, we find Mlle. Michonneau and Poiret at the Botanical Gardens in conversation with the mysterious man Bianchon had mentioned to Eugène. The man is M. Gondureau, a detective who is trying to get information about Vautrin, whom he suspects of being the escaped convict, Jacques Collin, nicknamed Cheat-Death (Trompe la Mort). Trompe la Mort, he explains, is a very dangerous man, a banker for the underworld, who handles his fellow convicts' money, sees to it that they get the best lawyers, and arranges escapes.
The detective tells the couple that the Minister of Police would like them to obtain positive evidence that Vautrin is Jacques Collin before the police move in on him, as they cannot afford to make a mistake. Collin has been branded on the shoulder, so if Poiret and Michonneau would give him a drug, the effect of which is that of a heart attack, they could check his shoulder for the brand. (Convicts were branded with the letters "T. F.," initials for hard labor.)
For the sum of three thousand francs, Mlle. Michonneau finally agrees to expose Vautrin.
On arriving at the boardinghouse, the couple notice Rastignac courting Victorine Taillefer. Eugène, quite upset by Delphine's cold attitude toward him and following Vautrin's suggestion, has turned to Victorine, thinking that only a miracle could now save him from degradation.
Vautrin comes in and tells Rastignac that the trap is laid and that the next day Frederic Taillefer will be killed in a duel, leaving his sister the sole heir to the banker's fortune. Before Rastignac, who is stupefied, can say anything, Goriot and other boarders come in.
Goriot asks the young man to his room and tells him that the reason his daughter sent Eugène away earlier was that she was expecting her father to come and that they had prepared a surprise for Eugène. They have rented an apartment for the young man on Rue d' Artois in a fashionable neighborhood, and all Goriot asks is to be allowed to use a maid's room belonging to the apartment so that he can be close to his daughter. Goriot explains to Eugène that he has had his lawyer arrange for Delphine to receive the interest on her dowry, on which the couple can live comfortably.
This is the miracle Eugène has been praying for. Now he can do without Victorine's fortune, and he plans to warn the Taillefers of Vautrin's plot.
When they come down for dinner, Vautrin is already there in a joyful mood, offering to treat the boarders to his claret wine. The dinner, owing to the effect of the wine, is going on boisterously when everyone notices that Eugène and Goriot seem drunk and are falling asleep. This is the effect of a soporific Vautrin has slipped into their wine when he overheard Eugène telling Old Goriot that he would go and warn the Taillefers. Victorine gets up to look after Eugène and helps the other women take him to his room. She is sure that Eugène loves her and feels "the happiest creature in Paris."
Another result of that dinner is Mlle. Michonneau's resolution to betray Vautrin. At first she was debating whether it would not be to her financial advantage to warn the convict, but when he calls her a "graveyard Venus," her mind is made up.
She meets the police inspector and tells him that she will unmask Vautrin the next day. The detective replies that they will be waiting with policemen and guards and that he hopes Vautrin will put up a fight, giving them an excuse to shoot and be rid of him.
This very complex section deals, at the same time, with all three plots in the book.
The detective story continues as we learn that the man Mlle. Michonneau and Poiret had been talking to is a detective, who suspects Vautrin to be, in reality, Jacques Collin, alias Trompe la Mort, an escaped convict, and offers the couple money if they will expose him. As greedy Michonneau is debating whether she could not obtain more money by warning the suspect, Vautrin makes the psychological mistake of calling her "a graveyard Venus." This insult, a deep-rooted allusion to Michonneau's past, seals Vautrin's fate. However, the suspense is kept up, for we do not know whether the arrest will be successful or not.
Rastignac's character evolves. We see pictured here his dramatic hesitation between Delphine and Victorine. The young man, upset at Delphine's playing with him, has turned to Victorine, although he knows that it means his full acceptance of Vautrin's plot and the murder of young Frederic. He feels completely lost when suddenly Goriot comes in and offers him an apartment and money, to be shared with Delphine. This is the miracle Eugène has been naively expecting; now he does not have to sell his soul to Vautrin, and he even will try, but in vain, to warn Frederic. Of course, the fact that he does not realize that this alternative is hardly more ethical shows his slow moral corruption.
Finally, we see Goriot's very pathetic outburst of paternal love, a sublime but animal-like and destructive passion. Pathetic, indeed, is the way Old Goriot is shown here as a dog, waiting to be petted. (This is an obvious Balzacian scientific reduction of man to a zoological figure, and it is noteworthy that every individual in Père Goriot is compared, at one point or another, with an animal: For example, Victorine is a wounded bird, Vautrin a wild cat.)
Also pathetic is the destruction of the old man's ethics. We have already seen that he likes Rastignac inasmuch as the young man has become a link between him and his daughter, that he has threatened to kill his sons-in-law, and that he is quite content to see his daughter live a life of sin, provided he can be with her to share it. Of Delphine, he says, "She has known no happiness, that excuses everything. Our Father in Heaven is surely on the side of fathers on earth who love their children."