After Circe has turned Odysseus men into pigs, Hermes advises Odysseus how to reason with Circe to get his men back. To refrain from being taken over by Circes sorcery, Hermès gives Odysseus moly. (A type of plant). He then tells Odysseus that he will have to bargain with Circe by staying with her for a year (and filling whatever desires she has..) in return for his men being returned to their natural human state. This obstacle was among the many that Odysseus faced on his journey back home.
I hope his helps! :)