The “huge key" that locks the strong exterior door of the tower is mentioned eight times in Telemachus. Stephen is keenly aware that Mulligan “wants that key,” and events prove him right: Mulligan asks for the key, and much later in the book he gives Stephen the slip and goes home to Sandycove without him. Stephen thinks of Mulligan at the end of Telemachus as a “Usurper," and in Proteus he thinks, "He has the key. I will not sleep there when this night comes." Giving up the key equates to homelessness for Stephen. This motif will eventually reach out to encompass Bloom and Ireland.
Joyce’s association of Stephen’s situation with Odyssean usurpation signals the possibility that keys may become freighted with symbolic significance, and the book does not disappoint this expectation. Bloom too heads out into the day’s business in Dublin without a key to his house, as a result of having left it in the pocket of the previous day’s trousers. Like Stephen, he has become symbolically unhoused, the usurpation associated in his case with his wife’s infidelity. In Ithaca he gets back into his house by “a stratagem” comparable to Odysseus’ stratagem for defeating the suitors, and he is described as a “competent keyless citizen.”
In Aeolus, keys begin to acquire another, related kind of significance. Bloom’s advertising campaign for a client named Keyes involves an allusion to the "house of keys," the lower house of Parliament on the Isle of Man. This elected body gave the island’s inhabitants a limited measure of home rule. By this "Innuendo of home rule" the key motif suggests that Ireland too, like the book’s two protagonists, lacks control of its own house.