The Amish are a charming people, gentle oddities in today's techno world. They don't do handguns, cars, or telephones, and they're exceedingly clannish in their desire to keep out technology generally and outsiders in particular. The basis for Witness is an age-old fish-out-of-water story: a modern man trying to fit in with the quaint Amish in Lancaster County, Pennsylvania. Taken on that basis alone, Witness is a success; it's when the "real" world intrudes, with its drugs and crooked cops and dead partners, that the movie falls apart.
Harrison Ford plays John Book, a big city cop who's more or less happy with the world and his place in it. A case comes to him just like any other case: A young Amish boy, Samuel Lapp (Lukas Haas, Mars Attacks!), is the only witness to a murder of an undercover cop in the men's room at a train station, and before you can say, "Police corruption," Ford's joined the boy and his widowed mother Rachel (Kelly McGillis, Top Gun) on their farm in Lancaster County.
He's hiding from his evil bosses (who kill his partner because he won't locate Book for them) and protecting the boy from them as well. Little Samuel Lapp is the only witness, you see, and Book really wants to get these creeps.
Of course, Book and the lovely Widow Lapp are attracted to one another. Problem is, the Amish don't take well to outsiders, and they certainly don't consider it meet that one of their own would become romantically involved with a big city cop who carries a gun and can't milk a cow to save his life. For them to be together forever, which is clearly what they'd both like, either he'd have to stay and become Amish, or she'd have to...