Inside, the company finds that the boys have just finished the sacrifice and are playing dice in the Apodyterium (an undressing room), with Lysis looking on. The men go and sit in an opposite corner of the room; Lysis looks interested, but doesn't actually come over to them until his friend Menexenus does. Hippothales stands out of view and listens, "lest he should anger [Lysis]" with his persistent presence.
Socrates opens the conversation with a few teasing questions as to whether Lysis or Menexenus is the older and which is the nobler, both of which are "matters of dispute" between the two). Socrates also asks who is the fairer, and at this the boys just laugh. Then Menexenus is called away to finish up some sacrificial duties, and the conversation with Lysis begins in earnest.
Now the dialogue takes the elenchus form, with Socrates asking long, sometimes disingenuous questions, and Lysis answering with short affirmations as he digs himself into an increasingly unsettling position. The issue is whether Lysis's parents keep him "in the condition of a slave." Socrates argues that they do (even while Socrates pretends to be shocked that this is the case): Lysis is not allowed to drive the chariot or even the mule cart, but the family's slaves are; Lysis's "master" (his tutor) is a slave, and so on.
Lysis is unfazed, and often laughs in delight at Socrates's crazy but apparently unassailable arguments. Finally Lysis replies that his parents treat him as a "slave" because he is not yet of age. Socrates then argues that Lysis is allowed to do many important things (read and write for the family, tune the lyre) even though he's young. Lysis then asks why his parents restrict his actions not because of his age, but because of his understanding (for example, he understands how to read and play the lyre, but not how to drive a chariot). This, of course, is what Socrates was getting at all along: "Yes, my dear youth the reason is not any deficiency of years, but a deficiency of knowledge."
Socrates takes this crucial point and extrapolates it, asking Lysis if not only his parents but his neighbors, the Athenian people, and even the king of Asia would grant him some degree of control if he was the wisest. The neighbor would commit the affairs of his house to Lysis if Lysis knew more about them than the neighbor, and so would the Athenian people. The "great king" would allow Lysis (rather than even the king's own son, the prince) to cook for him if Lysis was the better cook, and would even entrust the prince's vision to Lysis if Lysis knew how to heal eyes.
In short, everyone—"Hellenes and barbarians, men and women"—will trust Lysis in things that he understands: "these things will really be ours, for we shall turn them to our good." The opposite is true as well: even close friends will "hinder" us in matters we do not understand. In fact, if we have no wisdom, we will have no friends and no one will love us (even our parents), because we will be of no use to them.