Like the previous review, I can't say too much because to do so would spoil the fun. Regardless, Blood of the City is a fabulous read. The presentation of how magic and spells are used, especially the Cobblestone Druid (Urban Druid from Adv. Player's Guide), breathes a sense of fresh air into what is often formulaic spell descriptions.
Also if you ever plan on running or playing a Pathfinder game in Magnimar, the descriptions of the city are marvelous.
I rated it 4 stars because the one thing that annoyed me was some poor editing (a couple of wrong words used) and in the digital verson, some formating issues (like a comma in the middle of a word).
But this is the second Robin D. Laws book I have read in a week and have enjoyed every minute of it.