CURRYVILLE, Mo.  A troubled young man from this remote stretch of eastern Missouri, Chester Mast had traveled north in the summer of 2004 to stay with his extended family in Wisconsin. Mr. Mast, a member of a conservative Amish community here that eschews conveniences like electricity and telephones, was meant to apprentice with his uncle, a carpenter.

His uncle opened his home to the young man but, according to court documents, soon began having doubts about Mr. Mast. The uncle later told investigators that while traveling in Michigan he had observed his nephew, then 20, place his arm around his 13-year-old daughter. In the evenings back in Wisconsin, Mr. Mast and his cousins would open the windows and play cards in his bedroom. And it was there, investigators allege, that as the frogs croaked one summer night, the girl complained of a pain in her stomach.

“Chester convinced her that he could take her stomachache away,” James Small, a detective with the Waushara County Sheriff’s Department, reported in Wisconsin court filings. He asked her to lie on his stomach, the probable cause statement said. “She recalled being on top of him in his bedroom and that he ultimately penetrated her.”

These are but a few of the accusations that Mr. Mast, now 26, faces in a pair of sexual-assault cases that stretch between two states. The criminal charges, a rarity for a religious congregation that often resolves its disputes internally, offer an unusual glimpse into an Amish community in crisis. They have also laid bare the fault lines that divide this insular society that resides some 95 miles northwest of St. Louis.