"The Mortal Instruments" is a series of young adult fantasy novels written by Cassandra Clare. The story follows Clary Fray, a teenage girl who discovers she is part of a hidden world filled with Shadowhunters, demon hunters who protect humans from supernatural threats. The series explores themes of love, friendship, and identity as Clary navigates her new reality. The first book, titled "City of Bones," introduces readers to the Shadow World and its various creatures, including vampires, werewolves, and fairies. Throughout the series, Clary teams up with other characters, such as Jace Wayland and Simon Lewis, to confront dark forces and uncover her family's secrets.