FIRST of all, "Kingdom of the Wicked" is a misnomer. This book does not take place in the Kingdom of the Wicked. It does not explain the Kingdom of the Wicked. And if some social commentary were being made about how humans are more monstrous to each other than any demon of lore, you could have argued that the Kingdom of the Wicked is Earth...but that's NOT what happened here, the demons machinated everything, The Wicked were most definitely the wickedest wicked.

Secondly, and more importantly, this book is BAD, just categorically bad, and everything bad about it is revealed in miniature by its cheaply conceived title:
- The book doesn't talk about what it NEEDS to talk about. The plot is confusing, and all over the place. The world-building is non-existent; we get vague hints that maybe there's more to the history of witches and demons than dear Nonna relayed in her bedtime stories, but those discrepancies are never made explicit. And what should be THE highlight characters - be they antagonists or redemption arcs waiting to happen - are just... hot guys in suits.
- The protagonist can't follow clues to save her life, and she actively avoids things which might help her. She only stumbles into reveals and conflicts because her amulet plays magical Marco Polo with other active magic. And just like she's forced to feel magic at play, she is forced to feel emotions, as demons augment feelings in her which might not be her truth; meaning that when she has a change of heart, it is never because of character growth, but because her proximity to a certain demon has lessened! Emilia does not earn a single story, character, or emotional beat in this book. Why even is Emilia - the CLEAR author-insert - even the protagonist, when it's her feisty sister who is cutting deals with demons and unraveling the conspiracies around her coven, demons, and the church?! Clearly, Vittoria is the smarter, sassier, more daring, more interesting viewpoint character. Instead, we are subjected to her milk-toast sister, who gives us WAY too many descriptions of how to make pesto, or why she prefers romance novels to real life!
- It's redundant. This book repeats itself, and summarizes itself A LOT, for no apparent reason. I found myself, first, skimming whole paragraphs, because I didn't need the review session. Then, avoiding reading the book, because it was boring. To finally, falling asleep every time I tried to read.
- It has nothing to say. There isn't even any art to it, no metaphors... No message... A completely vapid tale about a girl who stumbles into whacky magical things, doesn't understand them, and then marries the devil because she runs out of things to stumble into.

Do yourself a favor: SKIP!