In Plain Sight by Marlayne Giron

It started with the crop circles followed by the disappearance of cattle. Then he appeared. He was obviously Old Order Amish. He did and said everything right but no one knew what family or farm he belonged to. He worked in the fields and barn raisings like everyone else and was in every respect just like one of them except for his silver eyes. Despite his quiet and respectful demeanor the community of Bird-in-Hand was leery of him. Every-one avoided him; except for Rebecca Esh...two star-crossed lovers whose romance not only endangers the Amish family who takes him in but puts the world he and his brother come from in great peril.