Twists and turns.
I don't know if this goes for everyone, but as a reader I enjoy being made to work. I like books where things are going on that I can't quite grasp, and I have to stop and muse a bit sometimes. I like it when the writer plays tricks on me. One brilliant example is a book I really admire, Christopher Priest's novel The Prestige. About a third into it I gradually began to sense that I was being hoaxed, or manipulated by the author. Read it, and you'll see what I mean. If you manage to work out what's happening, you, as reader, feel good about yourself and about the book too. And if you don't even notice, and the author completely floors you with some revelation later on, there's a strange pleasure in that too, I think.
With Incarceron and Sapphique I wanted to set up parameters and then blow them up. I wanted to place a few small explosive charges that would stun the reader as they travel through the book. If you've read them, you might guess which things I mean. Sometimes even I can't see these coming, which is good, as it means I can't give them away by leaving clues. What Attia announces about Claudia is one of those. I was as surprised as I hope the reader is.
It's probably quite perverse to enjoy leading the reader down one path and then whisking the very ground from under his/her feet, but it's fun.
The danger is that there's a fine line between being pleasantly puzzled or surprised and being totally lost and therefore bewildered. I know I tread that line sometimes, maybe at the end of Sapphique. I just hope readers still with me by then will be prepared for anything. I really
think that books should be an adventure, and challenge the reader and make them engage. That things which seem true may not be. That the boy tied across the transit lines may actually be part of the ambush. That the writer, who seems so nice, and to be telling a straightforward story, may be spinning you a whole sticky web of lies. Just like Finn.