Mariam is going to become a saint.
She lives in the pagan city of Chang'an. Her father is an agent who buys goods from merchants and sells them at a markup to the Chinese, as was his father, and his father before him. She doesn't talk to the Chinese; they worship demons, and her family locks the doors and prays whenever they're holding one of their festivals and demons walk the earth.
Mariam only rarely leaves her house; it isn't suitable for girls to be around men they aren't related to, even if those men don't worship demons. But her mother needs some goods from the market.
Mariam is feeling ill. Her confessor ordered more than the usual mortifications: she hasn't eaten anything but bread and water in three weeks, and she's still bleeding from where she scourged herself this morning. She should be tired enough from praying until 2am that she falls right to sleep, but she tosses and turns all night; the floor is hard, and her confessor hasn't allowed her her blanket.
It is Friday, and Mariam never eats on Fridays or Wednesdays, in memory of the Passion. So it isn't that surprising that on the way to the market she swoons in the middle of the street.