Richter Kless was the in-universe author of the Liber Chaotica, a collection of tomes that sought to explain the madness that is Chaos. Unfortunately, as was the case with all those who took to this task before him, he had succumbed to a curious sort of insanity that led to him seeing things that certainly shouldn't be witnessed by any ordinary man under Sigmar's protection, Inquisitorial Decree or not. Alongside its role of collating and documenting the innumerable forces of the Great Enemy, the Liber Chaotica also serves to document the decline of its unfortunate author's sanity.
The Liber Chaotica (as we have it) is a compilation of these notes by the order of an Inquisitor who sought to understand Richter's slippery slide.
A good chunk of this chapter documents the various tribes of Chaos Vikings, their lifestyles, and their peculiar customs in a detached, informative style. Beyond that is a discussion on how the warriors of the Blood God differentiate themselves from their peers, including their mutations and weapons (one of which includes a goddamn chainsword).
After a discussion on the similarities between Khorne and Khaine and a description of the Daemons of Khorne, shit gets WEIRD.
Through torturous visions, he sees the Black Crusades of Abaddon as well as the forces of the Khorne Berzerkers and the Daemon Engines of the Dark Millennium. The last segment documents an even stranger vision which is a (false) prophecy about the end of the world as we know it.
The first part of this book take to describing the nature of the Lord of Excess, in a way that's beyond just the meme-ridden "Drugs & Sex" business, and how one can even describe excess. Following that is a discussion on the Cults of Chaos: how they operate, who leads them, and how they manage to infiltrate civilized territories, as well how people get convinced to follow them. As it turns out, pleasure cults tend to stem from some innocent interests, like art and music.
The next part discusses a tale of two brothers, one who fell to Slaanesh and turned into...something less human, and one who joined Khorne and became a Daemon Prince. Following that is an in-depth description of an exorcism and the many rituals that take place during this occasion.
The most intriguing segment involves Richter's conversation with a debauched Bretonnian noble who formed his own pleasure cult before getting busted by the Witch Hunters and sentenced to death. This noble seems to hold no resentment or remorse for what happened, and doesn't so much as hate the Cult of Sigmar as he does find it completely boring. Instead, he tries to humanize Slaanesh and preach that the Chaos Gods aren't entirely evil. Indeed, he was so interested in Richter that he gives some poetry in hopes of convincing the author about his views.
Following that is a dive into the relationship between the Elves and the dark gods, how the Dark Elves are totally not Chaos, and in particular how Aenarion, first king of the High Elves, became a vessel for Asuryan. After this is a description of those tribes of warriors enslaved by Slaanesh, with particular segments dedicated to Styrkaar, Dechala the Denied One, and Azazel. His discussion on the daemons of Slaanesh are written as he finds himself again stuck in the Realms of Chaos, witnessing their pleasures.
A.K.A. the one where poor Richter starts losing it.
The first part of this book sees plenty of debate about the nature of despair, how Nurgle feasts upon it, and how to combat it, with one standout reference being a speech written by the Emperor Magnus the Pious following the Great War Against Chaos. An equally large part of this book has Richter working alongside a Sister of Shallya in treating the various illnesses she encounters, which has Richter himself bemoan the shitty health practices of the Empire, including how they treat those afflicted with a great illness. He makes a more passionate cry for help later on, damning the Empire's own ostracizing of the sick as empowering the Lord of Decay.
The research into the mortal champions of rot does not only see reference to human servants (Particularly Feytor the Tainted and Valnir the Reaper) and the Great War Against Chaos, but also give some overdue coverage on the Beastmen menace (with particular attention to the ravages laid by Gorthor the Beastlord). The discussion on the Daemons of Nurgle sees Richter dragged again to Chaos-land, though this time there are no references to the Death Guard or their Plague Marines.
The first chunk of this book sees Richter try to explain how the Great Conspirator works and how he has his cults organized (or rather, how they avoid being organized). In particular, he presents a paper documenting the damnation of Egrimm van Horstmann, former Patriarch of the College of Light and full-time heretic and cult-leader, as written by the current Patriarch, a former apprentice. Of course, this also includes discussing the viking legions of Chaos, with an article focusing on Aekold Helbrass.
The next part focuses on the nature of magic and how the Old World classifies the Winds of Magic. This of course also includes the Elf-exclusive winds of High and Dark magic as well as the differences between arcane magic and 'divine magic' (as Tzeentch calls it). After this is a paper written by that Bretonnian Noble from the Slaanesh Chapter challenging man's concept of evil and how man is responsible for making the Gods, a matter Richter discusses further in the next segment.
His segment on the Daemons of Chaos sees him visit a very angry red cyclops alongside the other daemons of Tzeentch. None of it is very pretty and coherence is pretty poor.
By this point, whatever sanity Richter had left has been abandoned. He has also mysteriously vanished, as the editor assembling this comments that he was nowhere to be found. No doubt that by this point, Richter was already on his marry way, journeying throughout the twisted Realms of Chaos to document an ever-shifting landscape. Rather than be a coherent tome, this is more a compilation of notes.
This last tome is effectively about Chaos Undivided and the process of how the Everchosen is made. Of course, this is made as an attempt to understand Archaon, the latest of the Everchosen, and how he got so twisted into serving Chaos.
The next part is a discussion about polytheism in general, breaking down the various gods of the Empire and neighboring nations, and how Sigmar is unlike them by being a man-turned-god. Of course, that crazy count from before returns with his own article explaining how Undivided might also just mean 'in service to a minor god without a realm', since this was pre-8th before Undivided as a concept was axed. Another article documents how Richter came to learn of Be'lakor, first and only Undivided Daemon Prince.
Richter in the End Times
As it turns out, we do find out that Richter didn't die in his quest. No, he has just gone very insane by the time he comes across Araloth and totally-not-Kaldor Draigo in their quest to rescue Shallya.