The story revolves around Ava, a student at Rosewood High School, who discovers a mysterious symbol in her art class and begins to investigate its origins. Along the way, she discovers a hidden diary that belonged to a previous student of Rosewood High and finds hints about the existence of a secret society within the school. Despite her friend Emily's initial reluctance to discuss the symbol, Ava learns that Emily is part of the secret society and becomes privy to its existence. Ava is drawn into society's world and uncovers the truth about its purpose and the mysterious symbol.

The story takes place in London between 2005 and 2010. Jack comes from a simple, middle-class family while Lily is from a wealthy family. They fall in love in junior high school.