Witness (1985)

An 8 year old Amish boy and his mother are traveling to Philadelphia, on their way to visit the mother's sister. While waiting at the train station, the young boy witnesses a brutal murder inside one of the bathroom stalls. Police detective John Book is assigned to investigate the murder of the man, who was an undercover cop. Soon after, Book finds out that he's in great danger when the culprits know about his investigation and hides out in the Amish community. There, he learns the way of living among the Amish locals, which consists of non-violence and agriculture. Book soon starts a romance with the mother of the little boy, but their romance is forbidden by the Amish standards. But, it's not long before the bad guys find out Book's whereabouts.