WADI NATRUN, Egypt — Christian monks living in the solitude of Egypt’s deserts have always faced the threat of attack from outside. In the early centuries, they built drawbridges and windowless towers to repel marauding nomads.

More recently, barricades and armed police officers ring the monasteries to guard against Islamic State suicide bombers, who target Christians.

But now, to the shock of the faithful, it turns out that danger also lurks inside the monastery walls.

The death of Bishop Epiphanius, the abbot of the fourth century Monastery of St. Macarius, last month has set off an ecclesiastical murder mystery worthy of a Dan Brown novel. More than a simple whodunit, the case has exposed simmering tensions of a theological, if not personal, nature in an influential corner of the Coptic Orthodox Church.