"Mercy" is a pretty straightforward urban fantasy in the vein of... well, a lot of urban fantasies. It's got a witch with a tragic origin story that drives the plot, an occult serial killer, lots of references to Salem (just down the road from the town of the title), neopagan magic, a witchfinder from the 17th century popping up in the modern day a la "Warlock," and destined true love with lots of passionate smooching. It is also (very definitively) just the beginning of a series, so if you're expecting all of this to wrap up neatly... or at all... by the end, you're going to be disappointed.
There's also a few nitpicks I have with the POV (it jumps into different characters' heads quite a bit) a cameo by a powerful magical entity, and the novel's portrayal of mental hospitals (which in no universe let out a guy with knife wounds claiming to be from another time just because his family asks nicely, nor are they fooled by someone hiding a pill in their mouth). And if you think the 17th century guy is going to sound like he's from the 17th century... no. Frequent nods are made to things he doesn't understand, but he drops modern phrases like any contemporary fantasy heartthrob. I'd grade the book down to two stars, but it has some strengths that made the reading experience breeze by.
The pacing is pretty good; the characters form a fairly convincing small town and seem real to one another; the heroes suffer a bit and have to struggle against some fairly powerful forces; and rather importantly, the central mystery reveals that not all allies and enemies are as they first appear. If you've read a lot of urban fantasies in which the hero finds out their True Lineage (tm), you probably won't be surprised by much here, but it came at appropriately dramatic moments. Lastly, I booed the characters that I was supposed to boo and liked the characters I was supposed to like, and that isn't the easiest thing in the world to write. So props to all the work that went into the book.
3 out of 5.