Psychopathic Villanelle—a young, beautiful, and prolific assassin—leaves a trail of high profile murders across several countries. MI5 officer Eve Polastri connects a new assassination to a series of such killings which she has been researching on her own time. Though her theory that the assassin is a woman is dismissed by her superiors, Eve's unauthorised interview with the only witness confirms it. Eve is fired, however, when the witness is murdered while under her care, along with a nurse and two guards. Impressed by Eve, Carolyn Martens, head of the Russia Section of MI6, recruits her for an off-the-books assignment to track the killer.