Of the twenty-one people who are specifically said to be present, three are known Sophists. In addition to Protagoras himself, there are Hippias of Elis and Prodicus of Ceos. Two of the sons of Pericles are said to be there, Paralus and Xanthippus. With the exception of Aristophanes, all of Socrates' named friends from the Symposium are in attendance: Eryximachus the doctor, and Phaedrus are there, and so are the lovers Pausanias and Agathon (who is said to be a mere boy at this point), and Alcibiades. Additionally, there are several unnamed foreigners whom Protagoras is said to have picked up in his travels and a servant (a eunuch) in the employ of Callias.
The dialogue begins with an unnamed friend of Socrates asking him how his pursuit of the young Alcibiades, just now reputed to be growing his first beard, was proceeding. Socrates explains that while he has just been in the company of Alcibiades, his mind is now on more interesting matters. He says that Protagoras, the wisest man alive (309c–d), is in town. Socrates relates the story of how his young friend, Hippocrates, son of Apollodorus, came knocking on his door before daybreak and roused him out of bed. Hippocrates was in a big hurry to be present when Protagoras held court, as he was expected to do, at the home of Callias.
Socrates warns the excitable Hippocrates that Sophists are dangerous. He tells him that the words of the Sophists go straight into the soul (psychē) and can corrupt a person straightaway. Socrates says that buying wisdom from a Sophist is different from buying food and drink at the market. With food and drink, you never know what you are getting, but you can consult experts for advice before consuming anything that might be dangerous (313a–314c).
Socrates says he regards Prodicus as a man of inspired genius (316a). He expresses the same admiration for Prodicus in another dialogue, the Theaetetus. Socrates later notes that Prodicus was assigned to sleep in a storage room that his host had cleaned out for the visit (315d).
Socrates accompanies Hippocrates to the home of Callias, and they stand in the doorway chatting about "some point which had come up along the road" (314c). A eunuch opens the door, takes one look at them, guesses they are Sophists, and slams the door in their faces (314d). They knock again, and this time assure the porter they are not Sophists, but only want to visit Protagoras. The porter lets them in, and it is at this point that Socrates recites the list of guests.