Wretched Wicked. Preternatural Affairs, #10

Cesar Hawke works for the Office of Preternatural Affairs. He's an agent in the Magic Violations Department, hunting down witches who break the law, saving lives, and getting caught up in a lot more trouble than he's paid to deal with. Fritz Friederling is his boss. The director. The heir of the Friederling fortune, earned by mining in Hell with human slaves. A man who puts away witches for life without trial.
Inheritor of his father's legacy, and his grandfather's, and all the ruthless men who came before. But they didn't always work together. Not before, and not after. Once they were strangers, and now they're something else. More fatal than family, more permanent than marriage, closer than the oldest friends, until death do they part... This novella tells the story of the early years of their partnership from Fritz Friederling's perspective.
It contains spoilers and should be read after the rest of the Preternatural Affairs series. It also includes a new, exclusive afterword from the author!