And here we have the whole comic.
Pirithous was the king of the Lapiths and a good friend to Theseus. Together they agreed to get themselves daughters of Zeus for wives. Theseus chose Helen of Sparta (who later would be known as Helen of Troy), and Pirithous somehow thought that it would be a good idea to go down to the Underworld to kidnap Persephone. Big mistake. According to one version Hades and Persephone pretended to offer them hospitality, and made them sit upon the throne of Lethe (Forgetfulness). Some say that Persephone later showed mercy and allowed Herakles to bring them back to the upper world, but most sources agree that only Theseus was allowed to leave and that Pirithous had to remain in the Underworld. And others say that none of them ever returned.
This comic was quite inspired by this lovely short story.