I have plans for a fantasy trilogy in which the main characters defeating the threat in each book simply makes way for the new threat of the next book. This way, the main characters can continue to grow and take on more powerful threats as the story progresses.
The way I have laid out the story so far ends with each book having a resolution. For example, the characters defeat the evil cult and celebrate. I plan on having this play into a twist, however, when they find out the cult actually was trying to prevent a catastrophic event from occurring that now the characters have to deal with personally.
The question is, where would it be ideal to reveal a twist of this nature? Should I reveal it at the end of the book where they destroy the cult so that the reader is more likely to pick up the next book? Or should I reveal it towards the beginning of the successive book where they are going to actually have to clean up after the mess?
Essentially, I am not sure whether leaving such a gaping cliff-hanger between novels is a good idea, because it could lessen the sense of accomplishment from the recent resolution.