If you ever wondered how to interpret Trinity Corebook rules - you NEED this book! It really is A MUST BUY for any Game Master / Storyguide in any Storypath game! Author clarifies or fix things that are vague or just problematic in oryginał corebook. If you ever had problem with players buying stuff - this book is for you. If you ever wondered how to build Advance Science tools and weapons - this book is for you. If you are dissatisfied with vagueness of base Trinity combat - this book is for you.