Critias tells Socrates that Charmides is his cousin, son of his uncle Glaucon. Chaerephon rushes over and asks Socrates if the boy is not beautiful, and Socrates agrees. Chaerephon says suggestively that if Socrates could see his naked form, he would forget all about his handsome face. Socrates says all this will be good and well if the boy also has a noble soul. Socrates tells Critias that before they look at his body, they will ask the boy to strip and show them his soul.
Charmides was Plato's uncle, his mother's brother. Critias, Socrates' other interlocutor, was Charmides' first cousin, making Plato Critias' first cousin once removed. Both Critias and Charmides went on to become important members of the Thirty Tyrants, the short-lived oligarchic regime that was established following Athenian defeat in the Peloponnesian War in 404 BCE, making the question of their sophrosyne, or moderation, alternatively ironic or pressing.
Charmides first suggests that sophrosyne is a kind of quietness (159b). Socrates talks him out of this, and Charmides proposes that sophrosne is the same as modesty. Socrates says this can't be right because Homer doesn't think so (160e). Charmides proposes that temperance is minding your own business. Socrates finds this particularly offensive, and tells Charmides that he must have heard this from some fool (162b). Socrates can tell from the uneasy look on Critias face that this was his idea, and they exchange some words. Socrates says to him testily that at his age, Charmides can hardly be expected to understand temperance (162e). At this point in the argument, Critias takes up the argument with Socrates suggesting that temperance might be the same as self-knowledge. Socrates confesses as they discuss this that his motive in refuting Critias is to examine himself, that he pursues the argument for his own sake (166c,d).
Critias' suggestion that sophrosyne is self-knowledge spurs Socrates to a discussion of the relation between medicine and science. He says that medicine is the science of health and disease, and that a person who does not understand these things is not in a position to distinguish a real physician from a quack (171c). He says that if wisdom really is knowing what you know and knowing what you don't know, no one would ever make a mistake, and we would pass through life without erring. He concludes that this does not happen, and that science is impossible.
Socrates say he dreams, however, of a world in which no one pretends to be something he is not (173a-d). In the end, Socrates appears to have recruited a new disciple to philosophy: Charmides says he is willing to be charmed every day by Socrates, and Critias tells the boy that if he is willing to do this, he will have proof of his temperance. Charmides says that if his guardian instructs him to submit to Socrates' charms, then he would be wrong not to do it.
Socrates' analogy, that ignorance is to the philosopher what disease is to the physician, is important and persistent in the dialogues. And everywhere, Socrates fails to effect a cure. In the Protagoras, for example, when the sophist Prodicus accuses Socrates of making a mess of their discussion, Socrates accepts the complaint and calls himself a laughable doctor ("geloios iatros"), whose treatment not only does not cure the disease, it worsens it (Protagoras 340e).
A variation on the medical theme is in the Theaetetus, where Socrates become a female doctor. Socrates compares himself to a midwife who helps boys and men give birth to their ideas. He says there that he (never having conceived of a viable idea himself) is barren, and has frequently had to commit the intellectual equivalent of infanticide (Theaetetus 160e).