Cousins Menedemos and Sostratos are preparing for a trading expedition to Athens. While philosophy-minded Sostratos is thrilled to return to Athens, Menedemos is both reluctant to leave his father's wife Baukis, with whom he has fallen in love, and relieved to be removed from temptation. They stock up on luxury goods and rush to Athens so Sostratos can make it there in time for Greater Dionysia, a parade and dramatic festival in honor of Dionysus.

In Athens, the cousins watch political history being made as Athens trades their sovereign ruler for an invader who announces plans to institute a newfangled "democracy." Meanwhile, Sostratos visits the Lykeion, the site of his unfinished education, but his fears of being mocked turn into triumph when he gets a good price for his wares. Menedemos, in typical fashion, starts an affair with a married woman, this time having the audicity to get their host's wife pregnant. In love as in trade, Menedemos's and Sostratos's quick wits have usually been enough to get them out of their self-created messes, but this may be pushing it...