An Unhappy Medium by Dawn Eastman

All of Crystal Haven, Michigan, is psyching up to participate in a Zombie Fun Run organized by Clyde’s nephew Seth, but Clyde is fretful about the undead festivities. For one thing, her sister, Grace, has unexpectedly returned to town after fifteen years. For another, Clyde has the nagging feeling that something is about to go wrong...
 
When one of the zombie runners is found murdered and then Grace disappears, Clyde realizes her grim premonition is dead-on. Now, she and her police detective boyfriend Mac must find a ghoulish murderer before someone points the finger at Grace. And when a tangled web of family secrets and old grudges combines with a mysterious case of stolen diamonds, even someone as quick-witted as Clyde might not be able to outrun a killer...