Billie is a recently retired member of “one of the most elite assassination squads on earth” (23) and was recruited for an all-female team of assassins by Constance. When the present-tense narrative opens, she is on a retirement cruise with Mary Alice, Helen, and Natalie—the other members of her squad—wondering what her life will become. She is skilled with languages and an expert in hand-to-hand combat, which she prefers to weapons because “I don’t like relying on something that can be taken away from me” (129). Most of the work’s flashback sequences focus on Billie’s missions and personal life, and the present-tense sections are from her point of view. This strongly implies she has compiled the manuscript and composed the author’s notes, reminding the reader of the secrecy surrounding the entire adventure.

Billie is a natural leader who dislikes boredom and is something of a thrill-seeker. She is recruited into the Museum because she has proven herself to be tenacious and intelligent, and she realizes during her recruitment interview she has no interest in marriage or children. She was abandoned by her mother and is largely self-taught in terms of her education, leaving college to pursue her career.