One of the series that I looked into, read and liked was P. L. Gaus's Michael Branden series. It begins with Blood of the Prodigal, which takes place in Ohio, where many of the Amish-flavored books are centered. The Amish (or “plain people") and the English (or "vain ones") share a county. Most of the time the Amish keep to themselves and solve their own problems, but when a 10-year-old boy is missing, the local police are called in at the behest of Bishop Eli Miller. A local pastor, Caleb Troyer, and college professor Michael Branden help the Sheriff investigate.
David Hawkins was once a soldier who was trained to kill by the U.S. military. In order to gain some measure of tranquility he contacted an Amish friend of his and did what was necessary to join the Amish community. He had been among the "plain people" for seven years when the tragedy of his daughter's murder struck him. A basic part of the Amish belief is that vengeance belongs to God and He will deal with it in time. Everybody is afraid that David has cracked and reverted to his old way of life, but David’s closest friends have grim faith that he is still abiding by the Amish pacifist ways.
Paul Louis Gaus lives in Wooster, Ohio, a few miles north of Holmes County, where the world’s largest and most varied settlement of Amish and Mennonite people reside. His knowledge of the "plain people" comes from exploring narrow blacktop roads and gravel lanes of the communities whose members live close to the "English" non -Amish people. There are seven books in this series so far.
While also taking place in bucolic areas of Ohio, the story begins with a flashback a description of the actions of a madman known as "The Slaughterhouse Killer" so graphic that is best read with your eyes averted. Unfortunately, what you miss on the first go-round is bound to pop up again and again for your edification. The lone survivor of that years-earlier series of brutal murders was Kate Burkholder, then a young Amish girl who left the faith and her home after the killings. Kate went into law enforcement in the city before returning to her home town of Painter’s Mill as Chief of Police. One snowy day, another body is found with all the hallmarks of a maniacal killing dealt by the Slaughterhouse Killer. Kate has to reconnect with her Amish family in order to solve this case before more girls are killed. In this novel, there is no respite from violence, four-letter words and the only sex is criminal. There are three novels in the Silence series; the next is Pray for Silence and new this year is Breaking Silence.
The Amish do have groups with varying strictness about certain aspects of their culture; no two sects are exactly the same, except in the basic religious beliefs. But, as one character puts it, we are human too. This aspect is dealt with by the Rumspringa, which allows adolescents a period of time to cut loose without condemnation, so that they can then make a decision to leave the community or choose a life commitment to the faith (as most do).