In Cold Blood, by Mark Dawson

This book is spin off from a series about a character named John Milton; in this volume, the main character is Beatrix Rose and we don't hear from Milton at all.

Let me cut to the chase: I'm not running to get the other books in the series.   If one of them shows up for free on Kindle, I will get it to read on an airplane.

Okay, if you're still interested:  Rose is an assassin.  She's angry with a bunch of former colleagues who betrayed her, killed her husband, and kidnapped her daughter.  Now, reunited with the child, she's out for revenge.

In Cold Blood (Beatrix Rose Book 1)