A bored but perceptive MI5 officer becomes obsessed with tracking down a highly skilled and unpredictable female assassin, while the assassin grows equally fascinated with her pursuer. The two women are drawn into an increasingly dangerous cat-and-mouse relationship that blurs the lines between hunter and hunted, professional duty and personal fixation. Their entanglement pulls both of them deeper into a shadowy world of espionage and violence, with each encounter raising the stakes of their strange mutual obsession.