It was three a.m. in Laugarvatn, Iceland, and I couldn’t sleep. Now partly that was because it’s still light in Iceland in June, and my circadian rhythms were bouncing all over the place. But there was a much deeper problem. Here I was, two thirds of the way through the first draft of my mystery thriller Killer Story, and doubt held me in its iron grip. Had I chosen the wrong murderer? That seemed impossible. This was my sixth mystery novel, and I’ve written lots of mystery episodes for Law & Order, CSI: Miami, Medium, and other shows. When I start writing a mystery, there are things I’m not sure of: who all the red herrings are, and what all the plot twists will be. But two things I’ve always known, absolutely: who gets killed, and who does the killing. The beginning of the novel/TV show, and the end. But now here I was, on my skinny little bed at the Gullkistan Artist Colony (great place, BTW; highly recommend), retracing the entire book in my head. I was finally facing up to the cold hard truth that my murderer didn’t really appear until page 80 of the book. I mean,…