There were sprinklings of different mythologies throughout the book, and Nyx even references a few herself while ruminating or talking to the Prince. They were inserted unobtrusively though, so you only had a niggling at the back of your mind... I know I've heard this story somewhere before... 
 There's a decent amount of world building, though I wish there more on the town than on the wallpaper and furnishings. I suppose it makes sense since the majority of the plot occurs in the house. 
 Nyx is a fun character; you can't help but like her even when she's whining about how awful she is. (Which gets a tad annoying. Your family sacrificed you girl, go ahead and be mad!) You have to wonder that her father raised her to defeat the Prince but didn't think to teach her a thing about self-control and not, you know, throwing dinner plates at his head. 
 Shade is a bit Shade-y. The author did a good job on giving him an ookie feeling from the get go. Nyx may have thought he was something special but I just thought he was creepy. 
 The Prince is the opposite of Shade, which makes sense [spoiler removed]. He reminds me of every rake in every romance novel ever, but in a really great way. 
 Nyx's family is a bit two dimensional. Her father is a bad guy because he struck the bargain that killed her mother and sent her to the Prince. I'd like to assume he's not all bad, but he's off diddling his wife's sister and doting on Nyx's sister so... who knows. 
 I enjoyed the book quite a lot and would have read it in one sitting if it weren't for those pesky adult responsibilities. I look forward to anything else this author puts out. 
 The plot... one big spoiler ahead. 
 Nyx (cleverly named after the Goddess of night) has been raised to marry the Prince of Demons and assassinate him. Her father struck a bargain with the Prince that his wife bear children and in return he would sacrifice one of the two to be the Prince's wife when she turned 17. 
 Nyx's father is part of a secret order intent on bringing down the Prince and freeing Arcadia, the land where they live. Arcadia has been cut off from the rest of the world, literally as if it was torn off the planet and placed somewhere else. The belief is that if the Prince can be defeated, Arcadia will be returned and they will see the sun and stars again. 
 Nyx has a twin sister who is NOT being sacrificed. Much of the book is about how much Nyx hates her sister because she gets to live while she must die. Seriously, a ton of the book is the whining about how she hates her, but she shouldn't, but she does anyway, even though it's not her fault, but does she have to be so naive about, but she shouldn't have to be unhappy...etc, etc, etc. 
 So, Nyx heads off to meet her new husband, the Prince of Demons. The Prince is super cute, as is his shadow. The shadow is kind where the Prince is cruel, and Nyx settles into a relationship with him. She sets about her mission to find the "hearts" of the house that she has to undo to bring it down. ( Magic stuff. Less important to the plot than you might think.) 
 There are doors she shouldn't go through, so of course those are the ones she wants to explore the most. The assumption is that the Prince wouldn't give her a key to a room with a heart. Shade (the Prince's shadow) shows her where one is, and later the Prince tells her it doesn't matter if she finds them because there is one she can't reach anyhow. 
 Nyx alternates between crushing on the Prince and Shade and hating herself for betraying one or the other. Some mad Stockholm syndrome stuff starts to take place but in a fun Disney way. (Think Beauty and the Beast.) 
 Shade turns out to be super evil serial killer type guy, so Nyx falls in love with the Prince. They gallivant about for awhile looking for the Prince's name or a way out of the curse. Eventually Nyx must go back and visit her mother's grave and then her sister. Her sister convinces her to kill the Prince and Nyx goes along with it, very Cupid and Psyche style. She comes back and frees Shade from where the Prince has stashed him along with these creepy demon things that kill him and suck him back up and free Arcadia just as the Prince declares he thinks he knows a way to break the curse on his own. 
 Nyx wakes up in present day thinking the whole thing was a dream since the Gods had gone back and redone the Prince's decision from the get-go. She doesn't want to forget, though, and goes and saves him and they live happily ever after. The End.