I'm not entirely sure as it could be about various things. It might be about dark adepts, who are often characters in a fantasy or science - fiction setting, dealing with their powers, their role in a particular world, and the challenges they face.
The Skaven are a race in the Warhammer universe. Their origin story is somewhat murky. They are said to have been created by the Horned Rat, a malevolent deity. They live in vast underground empires. They are generally a devious and treacherous race, always plotting and scheming, often against each other as well as other races. Their society is highly stratified, with different clans having different roles and power levels.
Once there was a skaven who thought he was a great inventor. He made a 'brilliant' trap to catch the local cats that were always stealing his food scraps. He spent days building it with all kinds of gizmos and levers. But when he finally set it up and lured a cat in, the cat just walked right through it as if it was nothing. The skaven was so confused and frustrated that he ended up chasing his own tail in anger.
One good skaven novel is 'Skaven Slayer'. It delves into the dark and devious world of the skaven, following the adventures of a slayer who is out to vanquish these rat - like creatures. The story is filled with action and intrigue as the protagonist battles against the skaven's numerous traps and schemes.
The Skaven origin story is one of dark and twisted beginnings. They were created by the Horned Rat. Long ago, the Skaven were a race bred in the dark and dank under-empire. They were designed to be a race of vermin, with a natural inclination towards chaos and subterfuge. Their society is highly hierarchical, with the powerful Grey Seers at the top, who claim to have a direct connection to the Horned Rat. This origin has led to their current state of constantly plotting and scheming, always looking for ways to gain power and expand their territory in the Warhammer world.
Since I don't know the specific 'dark adeptus novel', it's hard to say. But likely there could be the dark adeptus themselves as a main character, perhaps a mentor figure who guides them in their dark arts, and maybe an antagonist who opposes their actions.
One interesting Adeptus Mechanicus fanfiction could be about a Tech - Priest's journey to discover a long - lost piece of technology. They might face various challenges within the Mechanicus hierarchy and in the dangerous environments they traverse. Another could focus on the relationship between the Adeptus Mechanicus and other factions in the Warhammer 40K universe, like how they cooperate or conflict with the Space Marines.
Another great one is 'Skitarius' which focuses on the Skitarii, the cybernetic soldiers of the Adeptus Mechanicus. It shows their loyalty to the Mechanicus and their combat capabilities in various battle scenarios. The novel gives a detailed look at their weaponry and how they operate within the strict hierarchy of the Mechanicus.
One popular Adeptus Custodes novel is 'The Emperor's Legion'. It delves deep into the lore of the Adeptus Custodes, their unwavering loyalty to the Emperor, and their role in protecting the Imperial Palace. Another great one could be 'Custodes: Shield of Terra' which showcases their combat capabilities and the high - tech weaponry they use in battle.