Lily B. attempts to transform her social standing and escape a dull summer by befriending a glamorous new relative. Lily B. documents her daily life in a journal, aiming to capture the events that will eventually define her future fame. When her best friend leaves for camp, Lily feels isolated until she encounters the LeBlancs, a family she perceives as the pinnacle of sophistication. She navigates the tension between her own family dynamics and her desire to fit into this new, exciting social circle. The narrative is presented through Lily's personal, observational perspective as she maneuvers through the complexities of adolescence.

Readers frequently highlight the protagonist's distinct voice, noting that her dramatic observations provide a humorous look at the teenage experience. Discussion often centers on the relatability of Lily's desire to reinvent herself during the summer months. Critics point out that the pacing remains consistent, focusing more on character growth and social navigation than high-stakes action. Many readers appreciate the balance between the protagonist's vanity and her underlying vulnerability as she interacts with the LeBlanc family. The book is often cited for its lighthearted approach to the common struggles of middle school and early high school social life.