Haines has been tentatively probing Stephen, trying to learn something about his religious beliefs, his thoughts about Shakespeare, his thoughts about Mulligan — anything that will help him understand the strange Irish intellectual and perhaps be able to use him in his work. Stephen has no interest in this, however, and the questions just make him feel more and more isolated.
In these panels, Stephen concludes that he cannot stay any longer at the tower, that he cannot be a part of Mulligan’s bankrupt intellectual project, even though he paid the rent on the tower. [n.b. — in real life, Mulligan’s counterpart, Oliver St. John Gogarty, was the one who paid the rent.] He accurately guesses that Mulligan will ask him for the key, and he will become displaced and homeless.
Stephen’s dragging his ashplant, or walking stick, behind him further accentuates his feelings of powerlessness and impotence. He calls it his “familiar,” like a magician’s assistant, calling his name. Everything around Stephen seems to be crying out for him to take action, like his Odyssean counterpart Telemachus. Even Haines reminds Stephen that he has the power to be his own master, but Stephen doesn’t see it yet.