A thriller novel is long, so there’s plenty of room for many things to happen. I start with a premise, and I know the general direction of a story, although the trajectory might change as the story goes on. 
I don’t know how other writers write, but I write in a light trance. I just type what drifts through my transom, and this works well as long as I’m following a general trajectory. A few sentences become a couple of paragraphs, then they become a scene, which leads to another scene. Ahead, there’s a plot point I like and plan to hit. I know I’ll get there, because I always have before. Along the way, all sorts ideas will pop up.
In Spectre Black, an abandoned Circle K appears in the middle of the desert. There’s a militia checkpoint on an empty road. There’s a car that can barely be seen at night. And a grizzled rancher who hands out religious tracts….
Wait! Religious tracts? What does that have to do with my story in Spectre Black? Why’d this guy show up? To be honest, when he first appeared, I had no idea. After a while, it became clear. The guy was there to give my character a message. And he did it with a religious tract.
I’m not an outliner. I just follow the story. Sometimes I end up at a dead end and have to back out. But usually that doesn’t happen. For me, the story has already taken up residence in my mind. Like the Arabic word I love so much, Maktub:
“It is written.”
