Ivan leaves Alyosha and feels greatly depressed. He cannot understand his depression until he realizes that perhaps it is because of his deep dread of meeting Smerdyakov. He does, however, go home, but seeing the cook sitting in the yard, hopes to pass him without speaking. Strangely, however, he cannot and finds himself greeting his half-brother with great cordiality.
Smerdyakov confesses to Ivan that he too is troubled because of the rivalry between Fyodor and Dmitri for Grushenka. He also fears that the strain of worry might bring on an epileptic seizure. Furthermore, he says, he knows that Dmitri has learned the secret signals that Grushenka is to use if ever she decides to come to Fyodor. If such a meeting occurs, the results could well be tragic: both Grigory and Marfa are ill, and Smerdyakov fears that he is ripe for a seizure and Fyodor will be left alone to face Dmitri's wrath. Ivan wonders why Smerdyakov told Dmitri the secret signals and suggests that perhaps Smerdyakov has arranged matters so that Dmitri will have access to old Fyodor as soon as Ivan leaves for Moscow. Ivan, however, cannot be a watchdog for Karamazov, so he resolves to leave the next day for Moscow as planned. Smerdyakov insists that he not go to Moscow, that he go to a nearer town, but Ivan is firm and goes to bed without further discussion. The talk has left him exhausted, however, and he finds that he cannot sleep.
Next day, Fyodor pleads with Ivan not to go to Moscow, but to a town close by to sell a copse of wood for the old man. Ivan finally agrees and, as he is leaving, admits to Smerdyakov that he is not going to Moscow. The servant whispers mysteriously that "it's always worth while speaking to a clever man." Ivan is puzzled.
A few hours later, Smerdyakov falls down the cellar steps and an attack of epilepsy seizes him. He is put to bed and, as predicted, Fyodor is alone. He locks all the doors and windows and then begins his wait for Grushenka. He is certain that she will come to him tonight.
Leaving Alyosha, Ivan feels morose and dejected, emotions probably related to the guilt that he feels by associating with Smerdyakov. For even though Ivan does not realize it, he is subconsciously beginning to feel a certain duplicity in his relationships with the servant; the last two chapters, in particular, show how certain actions on Ivan's part implicate him in the murder of old Fyodor.
This fact is also important: Ivan feels a distinct loathing for Smerdyakov. He has entered into many philosophical discussions with him, and we learn that they have discussed such questions as how there "could have been light on the first day when the sun, moon, and stars were only created on the fourth day." Smerdyakov, in turn, has discussed things that would impress Fyodor, hoping to make an impression on him and contradict old Grigory. However, he has, we discover, taken most of his ideas from Ivan. Even the idea of the murder came from Ivan.
When Ivan meets the cook, he has planned to say to him, "Get away, miserable idiot. What have I to do with you," but instead he says, "Is my father still asleep?" This reversal suggests that Ivan is repulsed by this creature but is drawn to him at the same time. By the same analogy, Ivan is repulsed by the idea that his father will be murdered but seems also to acquiesce in readying the scene for the hypothetical murder.
In these last chapters, one can easily see how completely Smerdyakov has planned the homicide. We hear, first of all, that Dmitri has heard of the secret signals by which Grushenka is to come to the old man. There could, of course, be no reason for Smerdyakov to tell Dmitri about these signals except to lay suspicion on Dmitri when it is known that he was aware of such signals; furthermore, Ivan's ready acceptance of Smerdyakov's explanation indicates that Ivan is also eager to accept such an alibi. Second, Smerdyakov announces that he feels that he will have an epileptic seizure on the following day — the day that Ivan will be absent from the house. Third, Smerdyakov announces that old Grigory will be doped with some strong medicine that Marfa gives him and always saves a bit of for herself; soon both will be in a heavy sleep. Consequently, Smerdyakov has conceived a perfect setting for murder; he has even created perfect alibis. As he announces later to Ivan, everything had to go just as he planned it; otherwise, the murder never could have been accomplished. Ivan even recognized this when he said earlier, "But aren't you trying to arrange it so?" and tried to remove himself from direct responsibility. But ultimately Ivan must take his share in the moral guilt for his father's death.
At the end of Book V, most of the machinery is arranged for the murder. Smerdyakov pretends to have his seizure, old Grigory is laid up with illness, Marfa prepares the medicine for them both, and Fyodor anxiously awaits Grushenka.