Unfinished Business by I. Christie

On her way to her vacation campground, Claire Hanson, a detective in the Petima Police Department, picks up the enigmatic MaryLyn Smith. While at the campground, a series of unfortunate accidents befall Claire, and MaryLyn is never around when they happen. Claire chalks it up to coincidence, but when her RV is raided by law enforcement officials looking for planted contraband and Claire is severely beaten in the incident, she knows these aren't chance events. What she doesn't know is whether MaryLyn is involved or not.