This is one of the few times I wish I spoke Elvish, because the English language does NOT have words strong enough to describe the superiority of this story. "Awesome," "fabulous," "amazing," or "brilliant" just do not have enough oomph or ring of truth to how I feel. "Breath-taking" is only marginally closer to what I want to express. "Utterly perfect" might work. 
 Now, to be fair, I've been following the Riptide Opening Blog Tour, including interviews with Rhi and Rhi's views on gender fluidity. Rhi likes to write "genderfuck," so I couldn't help looking at the story with those eyes. But while it's in the story, it's so not the point of the story. At least, not overtly. 
 Black and Jhez make their living as Nightwalkers, selling their life-force, or chi, to (and stealing some in return from) low-level energy vampires, or lyche, but they are careful and use their finely honed skills to stay alive for over a decade, a very long time for Nightwalkers to not become used up gutter trash. They are particularly disenchanted with their father, who left them to rot in the gutter just before the Disclosure [of the existence of lyche to the human populace], at which point the structure of society changed. 
 Black thinks he's been entrapped by the local lyche leader after he nips a bit of the vampire's chi, not realizing that it is illegal or that it will create a link between the two that neither of them wants or can control. Monsieur Garthelle uses that link to coerce Black and his twin Jhez to spy for him on lyche politics, only then to become embroiled in the mystery of a murder under his roof. Figuring out lyche society and politics on short notice is impossible, and they don't have much time to unravel the intrigues, alliances, and politics before someone comes knocking on their door expecting... something. Payment? Retribution? Power? 
 But working for and having an aural link to Monsieur Garthelle slowly causes Black to realize that not all of the lyche are the monsters they're made out to be. We readers experience Black's distrust, distaste, and fear slowly evolve into confusion into grudging respect into trust. And the pull between them is magnetic, even when it's not there. I've rarely read more well-written turns of phrase where seething disgust at a forced, completely unacceptable situation is gradually and acceptably not only desired, but eventually impossible to live without. AND it doesn't come across as some flavor of Stockholm Syndrome either. Where other authors I've read struggled to make such a scenario believable, Rhi had no troubles at all in creating a truly believable and enjoyable slow build and deep burn. It was incredible. 
 Black is the real-time narrator of the story, so everything the reader experiences is as Black experiences it. There are no flashbacks and very few memories even. We find out fairly early on that Black and his twin are not entirely human, but only through the course of the story and Black's (and Jhez's) discoveries do we come to understand what that means. The lines between what is lyche, what is human, and what is between the two are solidly blurred, just as the gender lines are blurred. (Though this is never an overt thought or an outright comparison, I couldn't help but make it.) 
 The politics can be thick at times, and most definitely confusing, but that's intentional because it's all unfamiliar to Black. But just as it takes time for Black to understand, it takes the reader that same time. I was very immersed in the mystery along with Jhez and Black, so it was very well done in my opinion. 
 I recommend this to everyone, but I suspect this will be a "love it or hate it" book. This story has so many complex layers that it will be very thought-provoking or cause hemorrhaging for those who don't want to look deeper. It's dark and deep, but it has quite a bit of humor in it as well. While you're reading, think about the underlying truths interwoven into the story which aren't blatantly stated but are there. It's worth it. 
 One note about the cover: I like the cover, but it made me think that Black is much younger than he actually is. (view spoiler)[Based on descriptions in the story, he's at least in his mid-30s, but we don't know that until around halfway through. His age isn't really important (but for the fact that it underscores how long he and Jhez have been Nightwalkers), but it did surprise me a touch. (hide spoiler)]