In this installment of Percy Jackson and the Olympians, Camp Halfblood is in grave danger. Someone has poisoned Thalia’s tree, and the protection it provided the camp is wearing thin. Grover is off trying to locate Pan, but Percy keeps having dreams that lead him to believe Grover is in grave danger — as the captive of the Cyclops Polyphemus. Will Percy be granted a second quest to go and rescue Grover? Will there be anything capable of saving Thalia’s tree (and Camp Halfblood)? Find out for yourself when you read (or listen to!) this book.