Kreizler (Daniel Brühl) and Moore (Luke Evans) travel to Washington, D.C., Sara (Dakota Fanning) goes rogue in pursuit of the truth. Lucius (Matthew Shear) tells Marcus (Douglas Smith) a secret. Byrnes (Ted Levine) and Connor (David Wilmot) tighten their grip on the investigation. 
- Sara Howard: "Kreizler is on his way to Washington. He believes there may be some connection between our killer and the West."
- John Moore: "We've found something. There was a massacre in New Paltz. Be careful."
- Sara Howard: "Do you think it was an accident?"
Eliza: "His throat was cut from ear to ear."
- Captain Miller: "you must be half-crazy to do what he did that day."
Marcus Isaacson: "What exactly did he do?"
- Mozart Piano Concerto in D minor is playing on the gramophone at Dr. Kreizler's house. As revealed by Sara Howard in Ascension, this was the Piano Concerto he played as a child before getting injured.
- The episode takes its name from Psychopathia Sexualis by Richard Freiherr von Krafft-Ebing. It is one of the first texts about sexual pathology, particularly noted for being one of the earliest studies on homosexuality, sadism, and masochism.
- A copy of the book is featured in the third episode, Silver Smile, as one of Dr. Kreizler's textbooks.
- The episode covers from Chapter Thirty-one to Chapter Thirty-five of Part III of Caleb Carr's novel, with some changes and additional original scenes.