I'm not sure the premise must stand on its own in book two. The second is only a continuation of the first.

I don't read a lot of trilogies. I am more into the series. Let me follow my favorite characters through most of their lives. However, I do believe a trilogy is basically the same idea as a series. You have a main story line that must carry over through the entirety of the trilogy. You then have side stories that make your characters more human and tie all of them together in some fashion. These side stories don't have to relate to the main story line. The main one is the timeline on which they all live. The rest are their individual stories that can interweave and overlap but don't necessarily have too.


Case studies? J.R. Ward's Brotherhood Series
Patricia Briggs, Mercy Thompson Series
Kim Harrison's The Hollows Series

I was going to use Star Wars as the actual Trilogy but even it isn't a trilogy anymore. Do we even have the three and done series anymore?