The third book in The Night World series. Published in the UK as Enchantress. It is told in the point of view of Thea Harman.
Plot: Thea and Blaise Harman are witch cousins and are like sisters. There's only one slight difference: Thea uses white magic and Blaise uses black magic. Blaise uses her charm and magic to make boys do anything for her, including cutting themselves with razors and burning down schools. When they start over at a new school and Thea heals Eric Ross from a snake bite, Thea and Eric realize they are Soulmates. Blaise is jealous that Eric has chosen Thea, and worried that Thea is breaking Night World law to be with Eric. In a desperate attempt to protect Eric from Blaise, Thea accidentally releases an angry spirit, that kills one of Blaise's admirers. Thea and Eric try their best to capture the angry spirit by luring it. But Thea is wanted by the Circle because she is not allowed to use that kind of magic, and so is Blaise and Thea's friend Dani. Thea manages to tell them that Eric is in trouble because the spirit was with him. She puts the spirit back where it came from. The Circle tells her that she cannot love a human so she chose to drink the Cup of Lethe, a drink that erases a part of your memory, erasing Thea's and Eric's knowing of Night World. However, Blaise had switched the drink with iced tea long before, therefore neither forget that the Night World exists.