About the Yellow Fever and what happened to Mattie.
The city that Mattie is from is Philadelphia. She has lived there for a while and she doesn't intend on moving or even traveling, at least that was the plan until the Yellow Fever.
Mattie has always been close with her Grandfather and he is a very fit and active man, therefore, she was not expecting him to die. She was devastated and decided to go and find Eliza.
After Grandfather had passed away, Mattie set off to find Eliza. While she was on her journey, she found a little girl, named Nell, all by herself on the lonely streets of Philadelphia crying over her broken doll. Mattie later finds out that Nell's mother had died.
With Nell by her side, Mattie ends up finding Eliza! Eliza takes care of Mattie and Nell, and in return Mattie helps Eliza care for Yellow Fever victims.
Mattie ends up seeing her Mother again after her Mother fled the country looking for Mattie and Grandfather but they weren't at the Ludingtons farm where Mother was going. Mother ends up coming back and shocking everyone!
Mattie love interest throughout the book, named Nathaniel Benson, starts to paint more pictures for Mattie and gets approved by Mother at the end. Mattie's mother had never liked Nathaniel before but she came around and said that she was fine with their relationship. They end up shaking hands and Mattie is ecstatic.