Max Greengrass is a stringer for the New York Herald in 1893. He's paid by the column inch. With no regular salary, Max must hustle for his stories, and late one night he nearly trips over one. He finds four cats lined up neatly on a Greenwich Village sidewalk. They have no visible wounds but are quite dead. They've been killed and ritually arranged.
The story makes the paper and Max pursues it, from low dives to posh mansions, from a proper if eccentric society of refined ladies, concerned about the suffering of stray felines, to a bizarre conspiracy of churchly landlords and respected insurers who are getting rich by exploiting the misery of others. And it doesn't stop there. The facts he uncovers suggest dark ideas Max can barely contemplate, arousing suspicions that terrify him. He meets a source in a deserted saloon, only to find the man, apparently dozing, as dead as the cats that started it all. Soon Max's worst terrors come to life. The story Max is stalking now stalks him.
Like The Alienist, The Dante Club, and Time and Again, Michael Blaine's The Midnight Band of Mercy is informed by actual events. It resurrects scandalous facts long since forgotten or conveniently—deliberately—buried, about an outrageous crime that spawned ever greater ones that haunt us to this day.