Brook Nathans, one of the CIA's Special Operations Group's top operators is charged with finding and killing Enigma. But the only thing known about the assassin is based on analysis of a blood sample recovered from the scene of one of the hits attributed to the killer that indicates Enigma is a woman. Just as Brook begins her assignment, a second contract appears. An anonymous source has put out a contract for the death of any CIA or MI6 operator.

Even though her identity is a closely guarded secret, an assassin recognizes Brook on a crowded tram and tries to kill her. While she manages to kill the man, she realizes her agency has been compromised, forcing her to go off the grid. Operating on her own without agency support leaves Brook in a precarious position. She must find and kill Enigma while being chased by assassins looking to collect a bounty. But when she begins receiving text messages from a mysterious person who saves her life and informs her that much of her information about Enigma is wrong, she's left in a quandary. With no idea who is telling the truth and who can be trusted, her predicament has become truly devious.