He seeks relief by turning to the study of the Middle Ages (chapter one contains the first critical appreciation of Matthias Grünewald's Tauberbischofsheim altarpiece) and begins to research the life of the notorious 15th-century child-murderer and torturer Gilles de Rais.

Through his contacts in Paris (notably Dr. Johannès, modeled after Joseph-Antoine Boullan), Durtal finds out that Satanism is not simply a thing of the past but alive in turn of the century France.

Dave Langford reviewed Là-Bas for White Dwarf #88, and described it as "A lurid and influential book, containing that famous description of the Black Mass attended by Huysmans himself.

"[2] Norman Mailer wrote a screenplay[3] and a short story he adapted from it[4][5] based on Huysmans's Là-Bas entitled Trial of the Warlock.

[6] This work was translated into Japanese by Hidekatsu Nojima and published as a book entitled Kuro-Misa (Black Mass) by Shueisha in 1977.