The novel’s title, “Bye, Baby,” is a recurring motif in the narrative that illustrates The Shifting Dynamics of Friendship. The phrase first appears in the backstory of Billie and Cassie’s childhood friendship. Obsessed with the movie Dirty Dancing as teenagers, Billie and Cassie call each other “Baby” to show their affinity with the film's lead female character. By referring to each other this way, the girls signal the intensity of their friendship. The affectionate nickname and its meaning, known only to them, excludes others from their intimacy, demonstrating they are best friends. Thus, when the girls reconcile after an argument, Cassie’s parting words, “Bye, Baby,” reaffirm their special bond.

As the narrative progresses, the meaning of “Bye, Baby” evolves to reflect the shifting dynamic of Billie and Cassie’s friendship. After abducting Ella, Billie is reminded of the phrase “Bye, Baby” as it echoes the dramatic shift in their relationship. No longer representing intimacy, the motif describes an act of retaliation motivated by Billie’s anger at Cassie’s lack of loyalty. When Cassie turns to Billie for support, unaware that her old friend was the perpetrator of the crime, she reverts to calling her “Baby.” The changing significance of the motif illustrates how toxic Billie and Cassie’s friendship has become.