Black Lamb's Blood is a recent published work in the series, coming out shortly after the death of Roselyn Thorburn. The author of the book wrote it with the intention of rationalizing how Diabolists are a necessary evil and chronicles certain points in his life where he's encountered demons and his thoughts on the role of the those who would utilize them.
A copy was given to Blake Thorburn by a driver of the Mann, Levinn, and Lewis Firm for him to read as payment for a ride to Toronto. While acknowledged as propaganda, Blake doesn't deny that the author makes a point. He later uses it to bind Pauz.