More Dangerous Than Man

The main character's ambiguous motives kept me guessing. I'm curious what motivated the author's choice to make him so morally grey.

The story kept rushing forward, which made it hard to catch my breath. Was this a deliberate choice to heighten suspense or just the natural flow of the plot?

The plot twists kept me on my toes, but I wonder if the author mapped out the entire story beforehand or discovered the surprises as they wrote.