The Prophet from Ephesus — Caroline Lawrence

It's August, AD 81. Presumed dead by their families but wanted by unknown authorities, Flavia and her friends feel very far from home.
When news of more kidnappings reach them, and they discover that one of Miriam's twins is among the missing, the four detectives set out for Halicarnassus to help. Here they find the countryside is full of prophets who heal the sick and cure the lame - or are they merely tricksters and villains in disguise?