The Caster of Destruction picks up shortly after the end of The Invaders of the Great Tomb. Some details from the side stories in the previous book are relevant here, but it primarily continues the main story. Among Overlord fans who keep up with the original Japanese versions of the book, Vol. 9 is largely considered to be the best. The battle between the Kingdom and the Empire mentioned in previous novels takes place here in epic, fantasy proportions. That being said, there are a few faults in here that have more to do with translation quality than plot/characters.
Like the previous books, The Caster of Destruction is split into several parts. Each part shows different character perspectives and acts like a mini-story within the main story. The beginning is a bit slow as it builds up to the battle but speeds up as the war approaches. It does feel like as this series goes longer, we start to see more of the same. People underestimate Ainz and co. for <insert reason> and bad things happen to them. Many sections are from the POVs of these characters. It gets a little stale building up characters who readers know are likely to be slaughtered.
But when the slaughter actually commences, audiences will not be left bored. This is another installment in the series that hammers in a key point: Ainz is the bad guy. He may have been human once, but he is now literally a heartless monster. As the story goes on and more time passes, he seems to lose more and more of his former humanity. What he does, or orders others to do, to people continues to be horrific while he feels nothing. He is not without mercy, but his definition of ‘mercy’ is not exactly the dictionary definition.
SMALL SPOILER BELOW
One thing very irksome in The Caster of Destruction was a translation error. In this book, Nazarick becomes a country and Ainz gains a title as king. The country is called the Sorcerer Kingdom with Ainz known as the Sorcerer King. For whatever reason, the translation changed his title to King of Darkness and the nation to the Kingdom of Darkness. Which seems to be the most generic villain title in any work of fiction, ever. Considering the Overlord anime, which covered the events of this book last fall, successfully translated the Sorcerer King title correctly, I do not know what happened there. Granted it was still good to read this book given the budget issues the show had during season 3, but the mistranslation left the book feeling somewhat incomplete.