Maryam Rostampour and Marziyeh Amirizadeh knew they were putting their lives on the line. Islamic laws in Iran forbade them from sharing their Christian beliefs, but in three years, they'd covertly put New Testaments into the hands of twenty thousand of their countrymen and started two secret house churches.

In 2009, they were finally arrested and held in the notorious Evin Prison in Tehran, a place where inmates are routinely tortured and executions are commonplace. In the face of ruthless interrogations, persecution, and a death sentence, Maryam and Marziyeh chose to take the...