Lord of the Abyss is the fourth book and conclusion to the Royal House of Shadows series. This is the story of Micah, the youngest Elden prince, who has no memory of his life before becoming the Lord of the Abyss. Liliana, the daughter of the Blood Sorcerer, endeavors to find him and bring back his memory before time runs out and Elden is lost forever.This is the book I had been waiting for - the whole reason I started the Royal Book of Shadows series. I admit that I had high expectations for this book and Nalini Singh did not disappoint. I loved, loved, loved the story of Micah and Liliana. Lord of the Abyss is a take on Beauty and the Beast but, in this case, it’s Liliana who is the Beast to Micah’s Beauty, at least on the surface. Born with a hooked nose, straw-like hair and a limping gait, Liliana is no beautiful maiden. Micah, on the other hand, looks like the prince he is. But though she is not beautiful on the outside, Liliana shines with beauty from within. It is her pure and good heart, her generous nature and intelligence that are able to capture Micah’s interest and tame the wildness in him. Micah and Liliana are such rich and unique characters. Romance novels are often rife with cliches but this was delightfully not so with these characters. Neither has had an easy life. Liliana has been the target of the Blood Sorcerer’s cruel games and punishments since she was a child. But instead of becoming dark and twisted like him, she’s developed an inner strength that would rival that of any warrior. Lilian is willing to risk everything to right the evil that her father has committed. People make cruel jokes about her looks and whisper behind her back. It hurts but Liliana knows that outer beauty does not equal inner beauty. She is kind to all of the creatures and people of the castle, and isn’t afraid to stand up to Micah’s autocratic ways. And Micah, oh Micah. Big and handsome and covered in armor, a shield for both his body and his heart. He never had a chance to be a child, the spell his parents cast flinging him to the bowels of the Black Castle, in a sleep state until he was old enough to take over as Guardian of the Abyss. All he has ever known is the castle and his grim role of Guardian. Used to getting his way, Micah is demanding and sometimes a little spoiled. But he is also very generous and fair. Naive about the ways of the world outside of the castle Micah has an air of innocence about him. Neither Liliana nor Micah has ever had any real friends and both lead a lonely existence. An unlikely pair of kindred spirits, they are able to see something good and beautiful in the other that no one else does. The halls and grounds of the Black Castle really come alive in this book. Singh has created a vivid world in which to set Liliana and Micah’s love story. All of the books have been different in their setting and Singh did a great job of creating the unique and believable world of the Black Castle. From the dark stairways and dungeons to Jissa and Bard - all of these elements came together to form a new and interesting world. For the final journey to Elden, Singh conjured up a whole host of dangerous creatures for Liliana and Micah to battle. Some are scarier in looks than personality but all of them are strange and different and add to the rich landscape.The only slight, very slight, criticism that I have for the book is that the ending seemed a little rushed. Because all of the books had been leading up to this battle with the Blood Sorcerer, I was expecting an all out epic fight. What happens is still satisfying but isn’t as grand as I was expecting. I also thought that the siblings would play a larger part in the battle. It ends up being Micah’s fight though they all lend their powers to defeat the Blood Sorcerer. This is a very minor complaint, as the ending is still awesome and everything wraps up nicely. This is easily my favorite book of the series and I still sigh a small sigh when I think about Micah and Liliana.Lord of the Abyss is a great book and fitting end to the tale of the royal heirs of Elden. It’s a unconventional fairy tale that is sweet and passionate and utterly captivating. It’s a story that makes me believe in happy endings and I know that I will be coming back to it again and again. *An e-ARC of this book was provided free of charge by NetGalley.com. This, in no way, affected my opinion or review of this book.