N is for Noose by Sue Grafton

Early spring in the Sierra Nevada, bringing the usual driving sleet and snow.  Private investigator Kinsey Millhouse is on her way west when she detours into Nota Lake (pop. 2356, elevation 4312) to check out a new client.  And, stepping out of the car, encounters a chill she an scarcely believe.

Only 6 weeks have passed since Nota County Sheriff's detective Tom Newquist died of a heart attack.  His widow is sure he was keeping secrets from her - and she wants Kinsey to find out what he was up to in the final weeks of his life.  But no one is prepared to talk.  The town, to the last threatening redneck, loses ranks.

All that Kinsey can uncover is that Newquist appeared to lead an exemplary life so what could he possibly have to conceal?  She's on the point of giving up - and later she wishes she had.

For her next interview is with a masked attacker in her motel room, serving up serious physical damage as a warning.  And then there's a chilling new clue: a childish drawing a a thick length of rope - fashioned in a hangman's noose....