Sin has been a very very unlucky girl. 
 Being the only female Seminus demon, she has lived a very lonely life as a paid top assassin. Until recently only her brother Lore knew about her existence and he was trying to protect her as much as possible. 
 Lately the other three bothers found out about her and they try to protect her in every cost -especially Shane who has already lost another younger sister. 
 So, Sin is a Smurfette . I just love the following quote from the previous book "Ecstasy Unveiled", where Tayla and Wraith are trying to explain to ignorant Eidolon what a Smurfette is: 
 Tayla cursed under her breath. "I was just explaining to Eidolon that Sin is a Smurfette." 
 Wraith swung his big body around to study Sin with blue eyes that were very different from Shade's, E's. and Lore's. Sin's, too. "Nah. Smurfette is way hotter." 
 "What the fuck is a Smurfette?" Eidolon was seriously getting annoyed now. 
 "There's this cartoon called The Smurfs," Tayla explained, slowly, as though Eidolon were the child here. 
 "They're these little blue people, and they're all male. But one day a female shows up. She shouldn't exist, but she does." 
 Eidolon considered that for a second. "How did she get there?" 
 "An evil wizard named Gargamel made her," Tayla said. "In a lab or something." 
 "So you're suggesting that an evil wizard made Sin?" 
 "Of course not, silly. I'm just saying she's a Smurfette. A lone female amongst males." 
 Eidolon frowned. "Did the Smurfette mate with the males?" 
 "Dude." Wraith grimaced. "It's a cartoon." 
 Sin also has a deadly gift. She can create viruses in order to kill her victims and her enemies. One of her viruses is now out of control. It is a lethal new werewolf virus and Sin has just started realizing how stupid she was when she created it in the first place. 
 Conall Dearghul is a dhampire (a rear half-werewolf, half-vampire breed) and he is immune to the virus. The only thing that could be relevant to his immunity is that he tasted Sin's blood, when they had a little fast hookup in a closet at UGH (Underworld General Hospital). 
 Conall is hot as hell and he is oozing sexyness. He is the perfect much for Sin who has a wicked mouth and hidden golden heart. 
 The two of them will try to hide since Sin is the most wanted person in the underworld (and not in a nice way), while Eidolon and his team will try to develop a vaccine. Obviously they will fall in love. It is time for Sin to stop being so lonely and for Conall to make sacrifices in order to keep her. 
 Secondary stories which are included in the book: 
 - The love story between Luc (Conall's friend and warg) and Kar (Aegis agent and a girl with many secrets) 
 -The beginning of the story that is told in next book "Eternal Rider". 
 What can I say? This is one of my favorite books in the Demonica series. 
 Amazing world building, breathtaking stories. By far, it is the best series about Demons.