First author, then kung fu killer?

I had just watched the trailer, about 3/5 of the way in, I was sold. This movie looked like its going to be a fairly descent and probably well-executed movie. The author, assuming the main protagonist, is writing a book on a killer, and seems to be uncovering a dark conspiracy. Sounds unoriginal, but still might be fun to watch.

Then near the end of the trailer, we see this seemingly innocent author kicking ass; doing karate stunts, fighting lots of baddies, throws one over a balcony after having a Kill-Bill style tussle with him, and, in a short scene, shoots a guy on the floor.

What the hell? This could either be a major leak in the plot (assuming that the author was the bad guy the whole time and is really the killer or assassin), or probably going to be the dumbest twist I'll ever see when I check Restitution out. Any thoughts?