Relentless was on the fast track to being the kind of Urban Fantasy book I loved. If only the end chapters had been chopped off and been replaced with Sara saving herself. 
 So, we have Sara. She can heal any supernatural being or animal with a mysterious power that she's known about since she was a kid. I liked Sara. She was a bit stubborn, but she wasn't completely stupid or making idiotic decisions because "plot". Most of her logic had me nodding along, agreeing. Later we find out she's a Mohiri, a person with a demon inside them. Good! It should have been left there. 
 Nikolas is a decent hero. A little on the bland side, reminds me of Dimitri from Vampire Academy, but he does seem to have more personality than Dimitri. It's probably the cool composure. I do like how the relationship between Nikolas and Sara grows naturally, instead of "BAM! He's so hot! Gonna ditch the entire plot and drool now." They don't hook up at all, but you can feel the underlying tension. (Believable) Build up is a GOOD THING. 
 Peter and Roland are good guy friends and secondary characters. It's nice to see an author acknowledge that girls can have guys that are friends without secret crushes and unrequited love. Remy is great too, even though my heart broke when he and Sara had to stop being friends. 
 The story is a full of various plots that tend to weave together nicely. Sara's search for her father's murderer, the vampire, Eli, who is obsessed with her, shady people looking for troll bile, Sara's mother... not everything is explained, but the main plot of the book is resolved. 
 Despite all this, I had to knock a star off my intended four star rating. Why? 
 (view spoiler)[Because of the ridiculous ending explaining that Sara is a super special snowflake. She's half udine (Fae) and half Mohiri. Udine are water Fae that are incredibly beautiful and desirable that can perform healing magic. Sara never had female friends because bitches be jealous. Guys all want her because she's so irresistible. Eli was obsessed with her because of her udine blood. 
 Seriously, why? Vampires hunt young, untrained Mohiri, explaining why Eli would be after her. Sara not having female friends could be explained by something simple like her not wanting female friends. I didn't have any in high school either, and I don't have snowflake blood. Her healing could have come from being a Mohiri. Roland and Peter's initial crushes on her could have been omitted. A whopping ONE guy being interested in her could be explained by A GUY BEING INTERESTED IN HER. I honestly wanted to cut off the end of the chapter where Sara falls off the cliff, change it to where she never falls and helps take down the vampires with her friends, and the book ends with her leaving to live with the Mohiri. I did not need super special sexy water sprites for two chapters. (hide spoiler)] 
 So three (could have been four) stars.