Left to Loathe by Blake Pierce is Book 14 in the Adele Sharp Mystery Series.
Special Agent Adele Sharp continues to suffer in guilt for her part in the death of a serial killer who called himself "The Painter". The guilt haunts and taunts her and she needs to tell her partner and love interest Agent John Renee what she's experiencing, but she keeps postponing the encounter. After getting the courage to confess her struggle to him, she's stunned by his reaction, but he follows up with a troublesome confession of his own.
The two of them are thrust into what has grown to be a serial murder of prostitutes that sends them first to the depravity of De Wallen, Amsterdam. They have very little to go on, and it only gets worse as the clues and information are slow-going but move them to Germany after another death. Adding to their frustration, the killer has a type. That they happen to resemble Adele is just an added side-effect in figuring out why he's selecting them.
When one of Adele's suspicions turns out terribly wrong, it eventually leads to other sources of information that prove to finally be valuable.
There is one parallel hidden underbelly of this story that no one, especially John and Adele, will ever see coming much to the dismay and absolute danger for both of them, leaving this novel in a desperate cliffhanger.
The growing closeness of Agents Renee and Sharp is well-written and rewarding. The "American Princess" as John likes to call Adele and the dashing French rogue Renee are very different in their cultural beginnings, backgrounds, crime-solving, and former lifestyles, but they mesh and Adele gets to see the best of John which he's growing more comfortable making available to her. That she decides to reveal her conscience to him is a big deal for her, and he lightens her burden with his honesty. There's a key element in her same confession to her father, and it doesn't appear to end well.
I love this series, but I'm not a huge fan of these types of cliffhangers. I would rather read a longer novel to have the extent of these events resolved rather than dangling them at a critical point only to have to wait for the next edition of the story.
Father, you know hearts, minds, souls. We can hide nothing from you, try as we might. Lord, bless Blake and provide what's needed for more stories. In the Name of Jesus, Amen.