The dialogue begins with an unnamed 'friend' jocularly asserting that Socrates is in hot pursuit of Alcibiades. Socrates, while acknowledging the attraction he feels for Alcibiades's youthful beauty, states that his desire for Alcibiades has been sidelined by the presence in Athens of Protagoras, reputedly the wisest man living. Wisdom, Socrates suggests, is more beautiful than physical good looks. Socrates proceeds to relate how Hippocrates, another of his young friends, had awoken him that morning and excitedly announced the arrival of Protagoras. Hippocrates, who wishes to become wise (sophos) by studying under Protagoras, then suggests that Socrates accompany him to Callias's house, where Protagoras is staying. Socrates agrees, but as it is still before dawn, he and Hippocrates first discuss Hippocrates's reasons for seeking out Protagoras as his teacher. Their dialogue concerns the precise nature of what Hippocrates hopes Protagoras will teach him; as Socrates soon reveals, Hippocrates has little idea: Protagoras is a Sophist, but Hippocrates does not himself want to become a Sophist. Asked by Socrates what specific knowledge Sophists can impart, Hippocrates suggests that Sophists are those who are expert in making others into skillful speakers, but he is unable to state what it is that Sophists teach their pupils to speak skillfully about.
Socrates urges that Hippocrates be cautious: although he is prepared to surrender the 'nourishment' of his mind to Protagoras's professional ability, he is ignorant as to the quality of what Protagoras sells. Indeed, as Socrates points out, prospective pupils are trapped in a paradox: one cannot know what Protagoras teaches until one has been taught it oneself, by which time—if his teachings are bad—it is too late. Nonetheless, Socrates proposes that Hippocrates accompany him to Callias's house in order to hear what Protagoras (and what the other Sophists in town, Hippias and Prodicus) have to say.
Upon arriving, Socrates and Protagoras are at first refused entry, Callias's doorkeeper suspecting them of being Sophists. Socrates manages to persuade him otherwise, and the doorkeeper ushers them into the central space of the house, where Protagoras is surrounded by his disciples; Hippias is also present, as is Prodicus, both also attended by their followers.
At first, these preliminary scenes may appear to have little in common with the ensuing dialogue; in effect, however, they frame and introduce the fundamental themes of the Protagoras. That Socrates is distracted from his seduction of Alcibiades creates an opportunity (an opening in, or a cessation of, his desire) in which philosophy can take root. Philosophical thought, therefore, requires the adoption of a different attitude to everyday concerns, and must even displace these concerns—Alcibiades's attractiveness, for instance—to some degree. Socrates's abrupt awakening constitutes another such displacement. If Socrates is unperturbed about having his sleep disrupted, this is because it is precisely awakening that is here in question: Hippocrates wishes to be awoken to wisdom, but how should this best be accomplished? Socrates springs out of bed in his eagerness to assist Hippocrates in his search, and in doing so, he also acts as a guide for the reader in answering the question, 'how should we best become wise?'
Socrates obliquely approaches just this question prior to his departure with Hippocrates for Callias's house. While the explicit topics the two discuss (to whom should one entrust one's education, what is the value and nature of the skill that the Sophists teach) are central themes for the dialogue as a whole, the form of this discussion is more important than any conclusions that Socrates and Hippocrates manage to draw. Indeed, Socrates succeeds only in unsettling Hippocrates's unexamined belief that he can buy from Protagoras what he needs. As Socrates reveals, what he needs, and whether Protagoras can sell it, are crucial questions that Hippocrates has failed to consider. The explicit philosophical limit of this section is reached with Hippocrates's recognition that he is ignorant: "'Really,' he said, 'I have nothing left to say'" (312e). However, the mode of further investigation has already been established: the effectiveness of Socrates's dialectic (his question and answer method of reasoning) in unveiling unconsidered premises and fallacious arguments has been made clear. The dialectic, it appears, will somehow awaken us to wisdom.
This problem of method leads into the other key topic considered in this first section: the nature of sophistry, and the competing merits of different forms of reason. That the eunuch doorman mistakes Socrates for a Sophist may be humorous, but it is also significant. Metaphorically, at least, sophistry is thereby associated with an inability to produce anything of value; the vagueness of the aim of sophistic instruction matches the ambiguous sexual category of the eunuch. Further, Socrates must renounce sophistry to be admitted into the place of philosophy; some forms of argument appear to arouse the suspicions of the gatekeepers of the mind. However, of Plato's dialogues, The Protagoras is probably the most respectful of sophistry; certainly, Protagoras makes better arguments and is less ridiculed than most of Socrates's interlocutors. The doorkeeper's confusion of Socrates and the Sophists, then, also indicates that we should attend carefully to what it is that makes the two different.