Grover found two strong half-bloods named Nico and Bianca in Westover Hall,. hHe called Percy, Annabeth and Thalia who got there by Percy's mom. A manticore named Dr. Thorn captured Nico, and Bianca and Percy who tried to help them. Then Grover, Thalia, Annabeth, Artemis and her hunters arrived and defeated Dr. Thorn who got away and took Annabeth with him.