Circe is a witch or enchantress in the Odyssey. She turned Odysseus' men to swine when they drank the sweet nectar she gave them. Odysseus was the only one who drank the nectar and was able to remain human because Hermes gave him moli to eat to protect him from Circe's spell. Upon surviving Circe's spell without being transformed, Circe then told Odysseus she would only turn his men back into their human form if he would take her to bed. He did. He stays on Circe's island a year before traveling to the Underworld.
Odysseus discovers Circe’s house but chooses not to go there before informing his men. On the next day, he divides his men into two groups, and they cast lots to select the group that will venture to the house. The selection falls on Eurylochus, and together with his men, he makes his way to Circe’s home. On arrival, the men call out for the owner, and Circe emerges. All the men go in except Eurylochus. Circe offers poisoned drinks to the men, and when the poison takes effect, she turns them into pigs. Eurylochus, shocked and saddened, runs back and reports the matter to Odysseus.
Odysseus is forced to go to Circe’s house. Along the way, he meets Hermes, who offers him a protective charm that will work against Circe’s mischief. Circe tries to poison Odysseus, but she fails and instead falls in love with the valiant warrior. Odysseus takes advantage of the situation and has Circe reverse the spell on his men.
They stay with Circe for a year before they feel the need to continue with their journey. Circe decides to help the men and informs Odysseus of what he has to do to safely get back home. She tells him to first visit Hades and seek out the Theban prophet Teiresias for information. She provides Odysseus with instructions on how to reach Hades, handle the ghosts of the dead, and obtain answers from the prophet to aid him on his way home. Upon his return from Hades, Circe provides Odysseus with further instructions on how to conduct his voyage.
It is clear from the story that without Circe’s help and direction, Odysseus’s journey to Ithaca would not have succeeded.