At the beginning of Mercury Retrograde it has been 2 months since the events in Dark Alchemy. This time around Petra Dee finds herself battling a basilisk and a female motorcycle gang/cult who call themselves The Sisters of Serpens. I'll give you one guess what they worship. It's also been 2 months since Gabe last spoke to Petra. The ending of Dark Alchemy was rather heart wrenching as far as Gabe went and was the main thing that kept me reading this series.
While I did not find this book as good as Dark Alchemy I did enjoy it. What I enjoyed about it were the parts about Gabe and The Hanged Men. If there had been more focus on The Hanged Men and less on the giant snake I might have given this a higher rating. I'm not even sure I really liked the overall plot of this book. The parts with the giant snake felt like watching one of those Syfy channel B movies at times. I also kind of felt like the motorcycle gang/cult was a little pointless, and I never really cared about Cal or what happened to him. But I was very happy that Gabe got some resolution to his story line. I kind of wish this had just been a duology instead of a trilogy or series or whatever it's going to end up being, but I will probably stick it out and read the next book because I don't mind continuing on with Petra's and Gabe's story.