[sufue]

Pentecost Alley is about half-way through Anne Perry's Charlotte and Thomas Pitt series. It's $1.99 in the US right now.

Kindle US: https://www.amazon.com/dp/B0042JSOA8
Kobo US: https://www.kobo.com/us/en/ebook/pentecost-alley-1

Spoiler:

The murder of a prostitute named Ada McKinley in a bedroom on decrepit Pentecost Alley should occasion no stir in Victoria’s great metropolis, but under the victim’s body, the police find a Hellfire Club badge inscribed with the name “Finlay Fitzjames”—a name that instantly draws Superintendent Thomas Pitt into the case. Finlay’s father—immensely wealthy, powerful, and dangerous—refuses to consider the possibility that his son has been in Ada McKinley’s bed. The implication is clear: Pitt is to arrest someone other than Finlay Fitzjames for Ada’s demise. But Thomas Pitt is not a man to be intimidated, and with the help of his quick-witted wife, Charlotte, he stubbornly pursues his investigation—one that twists and turns like London’s own ancient streets.