This paper reevaluates the role of Adeimantus in Book 2 of Plato's Republic, arguing that his challenge to Socrates' view of justice—specifically, his interest in the influence of the outer world on our inner lives—serves a crucial yet underappreciated purpose in initiating the political project of the work. I suggest that it's due to Adeimantus' contribution in the Republic that Plato's wide-ranging inquiry into issues in ethics, politics, psychology, epistemology, and metaphysics hangs together as an integrated whole. A further benefit (...) of this reevaluation, I argue, is the way it illuminates Plato's assessment of poetry in the dialogue. This paper was delivered this past year as part of the Boston Area Colloquium in Ancient Philosophy. Comments are welcome but please do not cite without permission. (shrink)