Blue Heaven by C.J. Box

When sister and brother Annie and William happen upon a man being murdered while they are out fishing after school, it sends them on the run, because they know their lives are in danger. As children, they don't have any resources or a place to hide out, but taking shelter in rancher Jess Rawlins' barn just might save their lives. The killers--men who have retired from jobs at the LAPD--know just how to manipulate the town's sheriff and have no qualms about using violence to capture the kids. In Blue Heaven, which won the Edgar for best novel in 2008, Box writes a cat and mouse scenario that's hard to put down.