|“||You, my dear, have the makings of a sorceress. Like me.||”|
Circe purified the Argonauts after Apsyrtus' death, but demanded that Medea and Jason leave her place for she had divined through her magic what they had done and didn't approve in the least of their elopement.
Circe invited Odysseus' crew to a feast of familiar food, a pottage of cheese and meal, sweetened with honey and laced with wine, but also laced with one of her potions. She then turned them all into pigs with a wand after they gorged themselves on it. Only Eurylochus, suspecting treachery from the outset, escaped to warn Odysseus and the others who had stayed behind at the ships.
Odysseus set out to rescue his men, but was intercepted by Hermes, who gave him the holy herb moly to protect himself from Circe's potion and told him to draw his sword and act as if he were to attack her. From there, Circe would ask him to bed but Hermes advised caution, for even there the goddess would be treacherous. She would take his manhood unless he had her swear by the names of the gods that she would not.
Circe ran a magical beauty salon on an island in the Sea of Monsters. She sometimes went by the alias of C.C. Although she treated females to a spa treatment, she turned all males who came to the island into guinea pigs. She formerly turned them into actual pigs, but found them too hard to take care of. She had captured Blackbeard and his crew mates and kept the ships in harbor.
When Percy and Annabeth came, Circe turned Percy into a guinea pig by tricking him into drinking a magic potion. When Annabeth found out, she used Hermes' multivitamins to become immune to Circe's sorcery and free Percy from his curse and make their escape on the Queen Anne's Revenge. When trying to save Percy, Annabeth couldn't tell which guinea pig was Percy however, so she stuffed all of the multivitamins in the cage, indirectly freeing all of the pirates that were also captured.
Annabeth and Percy reminisce about their previous encounter with Circe, with Annabeth saying to Percy that he made a "cute guinea pig" much to his chagrin.Medea mentioned that Circe is her aunt, and that she had taught her the ability of charmspeaking.
It was revealed that Reyna and her sister, Hylla, were at C.C.'s Spa and Resort when Percy and Annabeth were there. After Annabeth gave the pirates Hermes' Multivitamins, they became immune to Circe's magic and subsequently took over her island, forcing Reyna and Hylla to flee.
In The Sea of Monsters, Circe was described to be a very beautiful woman with long dark hair braided with threads of gold and piercing green eyes. She wore a silky black dress with shapes that seemed to move in the fabric: animal shadows, black upon black, like deer running through a forest at night.
Circe is extremely glamorous. She hates men and believes that the only way women can get power is through sorcery. In the Son of Neptune, Hylla states that Circe was a wise, generous employer.
Circe possesses the standard powers of a goddess.
- Mystiokinesis: As the Goddess of Magic, Circe has absolute control and divine authority over magic, though not to the same level as Hecate. Her magic color is light blue and white sparkles manifested whenever she used her magic. She is considered an inventress of many spells.
- Charmspeak: Circe has the ability of charmspeak, which allows her to influence others with enhanced vocal persuasiveness. Her singing is said to "drift through the air like a lullaby" and has an alluring effect, given how Percy described her voice seemed to "lift (him) off the steps and carry (him) toward her". Around her house prowled strangely docile lions and wolves, victims of her magic. She enchanted Percy into drinking a potion that turned him into a guinea pig in The Sea of Monsters. Medea later claimed in The Lost Hero that Circe taught her charmspeak.
- Pyrokinesis: Circe has pyrokinetic abilities. She made a flame appear in her palm and dance across her fingertips in The Sea of Monsters.
- Transfiguration: Circe is infamous for her ability to transform any object or being into something else. During ancient times, she transformed men into pigs through the use of drugs and a magic wand. In the modern era, she has taken to transform her victims into guinea pigs through the use of a magical potion.
- Knowledge of Drugs: As revealed by Homer's The Odyssey, Circe is renowned by her knowledge in drugs and herbs. Some of them enables her to create potions which transform men into pigs.
- Weaving: Circe is an extraordinary talented weaver who works at a huge loom. In Homer's The Odyssey, she wove a vast divine tapestry that was described as "finely-made, lovely, and shining". In The Sea of Monsters, her hands were said to "weave colored thread back and forth with amazing skill", and a tapestry of hers was described to shimmer like it was three-dimensional.
- In The Mark of Athena, Chrysaor planned on selling Hazel and Piper to her as slaves or trainees. It is unknown, however, if Circe managed to take her island back from Blackbeard sometime after Reyna and Hylla left, or possibly she opened a new spa.
- She and her half-sister Pasiphaë share the same title: Immortal Sorceress.
- In mythology, Circe's parents were either Helios and Perseis or Aeetes and Hecate. This differs from her parents in the books, which is said to be Helios and Hecate. This is most likely a change made for the series.
- In the myths, Circe was said to have given enchanted food to Odysseus' men, causing them to transform into pigs after their consumption. Odysseus was immune to the food's magic only because he ate special herbs that were given to him by Hermes.