MI5 security officer Eve Polastri is bored in her job and yearns for a more exciting life. When a Russian politician is murdered, Eve is tasked with protecting the only witness and soon finds herself on a collision course with violent and extraordinary assassin, Villanelle.

In the aftermath of her recent assignment, Villanelle is ordered to take a break. Never one to do as she's told, she goes ahead with her next mission regardless. Meanwhile, Eve is given a dream opportunity to join a secret MI6 unit tracking Villanelle and the shady organisation she works for.

When Villanelle kills a Chinese Colonel at a kink clinic in Berlin, Eve and Bill travel out to investigate. While Eve and Bill chase up a number of promising leads, Villanelle enjoys the cat and mouse of their proximity. But as they draw closer, Eve comes to realise that this is much more than a game.

Intel from Berlin points to the existence of a mole, prompting Eve to undertake her first surveillance operation. Meanwhile, Villanelle is sent to England to eliminate a member of British Intelligence. Villanelle wonders, could it be Eve? Meanwhile Eve, in emotional turmoil, now knows how high the stakes are.

Having survived a terrifying close call with Villanelle, Eve now has the mole ensconced in a safe house and is buzzing. They have an exciting opportunity to glean information and crack this thing open. But Villanelle hasn't finished with Eve, and boldly forces an escalation in their relationship from which there can be no return.

A female assassin is taken into custody in Russia, and Eve and Carolyn head out to Moscow to negotiate access. She could hold the key to the organisation that runs Villanelle. Meanwhile, Villanelle is smuggled into the same Russian jail. It's a grim and brutal place, where not even Villanelle is safe.