How to keep a surprise

My writing task for today is not to give too much away.

I'm getting towards the end of Panthera: Death Song.  My characters have now reached the location where the final reveal of what's been going on all through the book is discovered.

It's a tricky balancing act not giving too much away.  Because this is the second book, there are links to what happened in the first one, Death Spiral, but I'm trying not to give away what happened in that book in the second one, in case readers read them out of sequence.  But for the characters, there  is a link between the adventures in the two books, and they would naturally make comparisons to the two situations.

I know what the answer to the mystery is, because I worked out my chapter plan before I started, but I have to make sure I don't give away too much too early.