Jason, Piper, and Annabeth arrive at the "out-of-control zombie frat party" (2.1)—Odysseus' palace, not college.
Disguised as an old man, Jason sidles up to one of the banquet tables.
A ghoul named Antinous confuses Jason with Iros, an old beggar, and Jason rolls with it to get information from the ghouls.
He learns that all these not-so-super ghouls and ghosts believe that once Gaea is raised and destroys the gods, she will divide up the mortal world among them. They all want to be in Gaea's good graces.
One of the ghouls has really loose lips, and he lets slip that the good guys' ship will sink if they try to travel through the Straits of Corinth. The only safe way to the Acropolis, where Gaea will awaken, will be to take the long way around the entire Peloponnese.
Having the intel he needs, Jason makes his getaway. But one of the ghosts, a dead Roman praetor demigod named Michael Varus, stops him.
He sees through Jason's disguise, and he summons a ghost to stop Jason: Jason's own mother.