Mystery at Dead End Farm, Paperback/Mary C. Jane

A potato farm in Maine is a dreary enough place to visit, city-bred Priscilla reflects gloomily, but how could her mother and brother, Lee, consider living here? Nothing exciting ever happens in Aroostook County...until the day the windmill on the farm next door stops turning. Standing there like some stricken monster, it lends the whole landscape an atmosphere of eerie menace. And its owner, the eccentric farmer and inventor, Nils Gustafson, has vanished, apparently into thin air. Rumors fly as neighbors try to account for the mild-seeming old man's mysterious disappearance. Lee and Priscilla, with their cousin, Greg, have their own theories. When they discover an ancient feud, an Indian plot, and a lost silver mine, they find themselves in real and spine-chilling danger!