Percy Jackson
In the third book, Grover finds two demigods at a school, Bianca and Nico di Angelo. Percy, Grover, Thalia and two of Artemis' hunters, Zoë and Bianca (who later chose to become a hunter, upsetting Nico), are sent on a quest to save Artemis, who has been kidnapped. Percy is really going to save Annabeth, who was captured while they were saving the di Angelo's.