So, I’ve got a GM who just started running this with a group of us online due to the pandemic. However, I can’t find which books he / we need access to in order to run this. I’d buy the actual AP, but I’d rather avoid spoilers. (And yes, I realize I could just get the info from the Nethys site, but I like supporting Paizo when I can.). So, aside from the core rule book, what other books are used in this AP?