The latest in Fraser's ``Green Grown the Rushes-O'' series (Symbols at Your Door, 1991, etc.) takes DCI David Webb back to his hometown of Erlesborough--and to a murder case he'd rather not solve. The catalyst is Webb's sister Sheila Fairchild, who as a child had once seen a ghost--a shrouded figure rising from a grave--she mentioned to her friends at the local coffee shop. Hours later, old Billy Makepeace, who'd overheard her story--a farmer who'd been feuding with her late father since before she was born--had broken a lifetime habit and phoned her. Before she could return his call he was dead, drowned in what turns out to be a suspicious accident. Clearly Billy saw more in the ghost story than Sheila did herself; but when Webb traces the ghost to a third rival of his father's--Dick Vernon, who stepped out for cigarettes a few days after his sister died and never came back- -he's left with another unsolved murder nearly 50 years old, a murder whose prime suspect is his own father. A disappointing solution, but put over with real ingenuity and deeper feeling than Fraser usually evokes in this uneven series.