Deadly Edge by Donald Westlake writing as Richard Stark (1971) Random House

Parker is just as ready to be mean as ever.  This time he’s protecting the woman he lives with.nbsp; He and a crew knock off the last show of a music venue.nbsp; They were one guy short because the guy just didn’t have it in him to do the job.nbsp; But after the money is split, they find the guy has been murdered.nbsp; Then another guy gets killed.nbsp; Parker’s contact calls him at his new residence, which he did not share.nbsp; Now Parker has to find whoever is doing the killing and stop them.