Protagoras

Protagoras is a lively and often humorous look at virtue, knowledge, and the best means of acquiring them.
Ostensibly a debate between Socrates and a sophist opponent over the education of a young man, the dialogue also concerns the nature of the contest itself. As told in retrospect by a somewhat frustrated Socrates, he is asked by Hippocrates to broker an introduction to Protagoras, a famous sophist with whom the young man wants to study. Socrates then begins a public debate with Protagoras in order to see what the sophist has to teach. The two men examine the nature of virtue - whether it can be taught, and whether all virtues are connected - but end up in conflict over their styles of discourse. Plato contrasts the crowd-pleasing oratory of Protagoras with the difficult and unglamorous questioning used by Socrates.
The multiple layers of conflict and discussion make Protagorus one of Plato's most dramatically satisfying works, and an excellent starting point for those new to his philosophy.