Rachel Elizabeth Dare
In this book, Rachel first appears at the Hoover Dam (in which they have a dam problem). Percy is being chased by a group of Spartoi when she sneezes. Percy turns around and his sword, Riptide, goes through her body. He realizes she knows it is a sword. He also finds out that she can see through the Mist. She saves Percy from the Spartoi by sending him into a restroom behind her and the skeletons to the generator room, which makes electricity.