This book is tagged with the "fantasy" genre, but while there are elements of magic and mythological creatures within it, this barely qualifies as a fantasy book. It is set in an alternate version of Portugal, and while well-described enough, the setting is just there, there is nothing about the place that blends into the story or adds anything special to it. It is nothing more than a turn-of-the-century, plodding investigative mystery, where the characters just happen to be sea creatures, selkies and sireia (sirens). 
 There is nothing that I outrightly hate about this book. You will notice I have no quotes of this book in this review; that is because there is nothing in this book that is worth quoting, for better or worse. The characters are fine, the world building is lacking somewhat, the mythology has inconsistencies, but it didn't really bother me that much because this book suffers from a glaring problem of having a really, really boring plot and a completely underwhelming mystery with no intrigue and no danger whatsoever. 
 Summary: Oriana Parestes is a sireia (a siren) who lives as a maidservant to Lady Isabel in The Golden City, a fictional city in an alternate version of Portugal. It is September 1902, and they are running away from home so that Isabel can elope with her lover. Barely out of their house, the two are abducted, and they wake to find themselves in a miniature underground version of Isabel's mansion, tied and trapped in an underwater artwork installment known as The City Under the Sea. Thanks to her heritage as a sireia, Oriana manages to escape, but Isabel is not so lucky. After her escape, Oriana is found and taken under the care of a wealthy society young man named Duilio Ferreira who dabbles as a police consultant. He is part sea creature himself, and together, the two set out to investigate the mystery of her disappearance, of his mother's missing pelt, of some kind of mysterious conspiracy against the king. And there's some vague stuff about spying. 
 The plot: So extremely dull. Don't get me wrong, I love a good mystery. Mysteries are my bread-and-butter of reading. I absolutely adore mysteries, but it has got to be well-written, it has got to be compelling, it has to have enough mystery and intrigue and danger, combined with excellent characterization to get me hooked. This book does no credit to the investigative genre. It is the worst kind of historical detective novel in that the investigative style is pure footwork, dull, boring, where the detectives themselves are so lacking in personality that there is nothing to keep me interested. 
 The book is so light on fantasy. The characters are sea creatures, with some minor powers; Duilio himself has the power of foresight if he happens to ask the right kinds of questions. Duilio's gift is in foretelling, and he has to ask himself questions in a certain way to get the right answers out of the voices in his head. I really would not call this book a fantasy at all, it is more of a mystery with some light fantasy elements that doesn't add anything to this book. It certainly does not make this book wondrous, magical, in any way whatsoever. 
 The book plods on as Duilio hires investigators, work with the police force, talk to servants and townspeople to get clues. Oriana goes to society parties to find more clues. It may be appropriately investigative, but it is just. So. BORING. There's something about necromancy, about dead servants being killed, but it is made so light as to seem everyday. It's like "Oh, I'm having a croissant this morning. The weather is particularly good, don't you think? It's been so rainy late, I'll be glad to see some sun. Oh, and there's someone maybe using necromancy magic to make the buildings in The City Under the Sea float underwater. Do you want to go for a walk today?" 
 THERE IS JUST NO DANGER. NO EXCITEMENT. It completely kills the element of mystery. I do not have a problem with historical mysteries. I know investigative methods of the past are old fashioned, slow, often without results. There is a way of making characters stand out, of following clues and making small details and everyday detection intriguing, compelling. This book completely fails in that regard. 
 Oriana is supposed to be a spy. I see no evidence of it. I see Oriana being worried somewhat about her father. I see her arguing with her spymaster, who is about as useful as boobs on a man. Oriana is supposed to have a destiny among her people, a gift for calling, which leads to her becoming a spy in the first place. The problem is simply that Oriana never, ever, ever acts as a spy. It is a title. Much like "Vice President." Sure, it seems pretty cool, but it's just for show only; everyone knows Vice Presidents are useless, much like Oriana's role as a spy. 
 Truly, this is the most boring mystery I have read this year. 
 The setting: Full of inconsistencies, plot holes, and while well-explained, without a true sense of place. The setting is in an alternate version of Portugal; the year is 1902. It may be Portugal, and it may be pretty well described, but the setting is largely irrelevant, and we are pretty much told "this is how things are" and told to accept them without much explanation. There is really no sense or reason for the setting. The book might as well have been set in Indonesia, Toronto, Chicago. The setting just doesn't really matter, however well the Golden City is described. The Golden City is a city within Portugal, ruled by a Prince Fabricio. Here is where things get fuzzy. We know that there's sirens, and otterfolk, and selkies. It took awhile for me to understand that people in Portugal actually knows of their existence, and it took awhile for the Sireia's past to be brought up. There's some light magical elements, and we know of otherworldly creatures, yet the people of this world seem strangely resistant to the idea of magic and often outrightly deny what's in front of their eyes altogether, while having laws adamantly against it. 
 There are just a lot of holes in this world, in its people, in their beliefs, in society. For example, sireia, selkies, otterfolks are banned on land. People are supposed to be suspicious and out to look for spies from the sea people, yet it is so easy for Oriana to blend in, and instead of suspecting that she's a spy (since there should be an atmosphere of a witch hunt), people too easily buy into the idea that Oriana just as psoriasis, since she's constantly covered from head to toe, instead of looking at the obvious "SHE'S A SEA CREATURE WHO HAS TO COVER HER FINS." 
 This is where the book disappointed me further. While her people's clothing, their history, is somewhat described, their society is left so incredibly vague. Oriana's people are supposedly matriarchal, and Oriana's father is in exile because he dared to challenge the fact that his gender is not inferior, yet Oriana is under the almost absolute control of a male head spymaster, and seems to be unable to challenge this. The mythology of the sireia, their culture, their society, is so incredibly vague. While it would not have contributed to the storyline, I would have loved to know more about her people, because at least I would have felt like there is more to Oriana that is worth knowing. 
 The characters: This book is narrated by two alternating characters, Oriana and Duilio. Both stories are told from a third-person narrative, and both characters are equally forgettable. Oriana is not stupid, she is simply without personality; as I said, she is spy in name only, a character on paper only. Oriana is not stupid, she is pretty smart sometimes, she never acts in a way that makes me want to bash her on the head for her idiocy, but she is altogether inconsistent in her characters sometimes, and I never, ever feel any sort of emotion from her or for her, even when Oriana witnesses her close friend's death and survives that attempt at murder herself. 
 Yes, she's sad about Isabel's death, but I never felt her sadness. It is just words written on paper, I never felt the overwhelming grief, the sense of injustice, the outrage that comes with wanting vengeance. Oriana's emotions just seem, for lack of a better word, false. You want a good demonstration of grief? Look at Mackayla Lane from the Fever series. Oriana's supposed grief is but a washed out pretense of it. 
 Duilio is a gentleman, but he is a contrary gentleman. I don't know what to think of him. Here is a guy who thinks nothing of bursting into Oriana's bath while she is naked to prove beyond a doubt that she is, in fact, a sireia, while thinking he's too chivalrous to take her to bed or to keep her as a mistress. He is, again, boring, and I can't help but feel that his and Oriana's love story is less of a love story than further proof that birds of a (boring) feather sticks together. Their courtship largely consists of shared glances while traipsing around town investigating stuff. Their romance burns as hot as a spluttering matchstick-sized birthday candle. 
 Skip this book unless you have a high tolerance for boredom. There is no fantasy here. The only mystery is how I managed to read this book without falling asleep.