Codename Villanelle by Luke Jennings
Codename Villanelle stars two women, a top-level assassin and the former MI6 operative whose job it is to find and eliminate her. Both women are strong and well-drawn. Villanelle is a psychopath, but one who knows she's different and uses the knowledge as a strength. Eve is a tough, but has more connections. she has a husband and subordinates; her choices effect not only her life, but theirs too.
This is an action story, full of violence and sex, but happily it never quite tips over into graphic or gratuitous. It's a quick read and I enjoyed it, right up until the end. I guess this a collection of 4 novellas. It felt seamless to me, but then it ended with more or less "to be continued," which always just annoys me. If your series is good enough, I will continue to read it without a middle school book trick. Give me a semi-conclusion and leave it there. I'll know the...