Kathleen Fuller.  The Promise of a Letter.  Thomas Nelson, 2017.  See here to buy the book.
The Promise of a Letter is Book 2 of Kathleen Fuller’s “Amish Letters” series.  The first book, Written in Love,
 was about Jalon, Phoebe, Phoebe’s child Malachi, and, last but not 
least, Blue the cat.  Book 2 focuses on Leanna, who is the sister of 
Jalon, Roman, Roman’s brother Daniel and his wife Barbara, and Karen and
 Adam, a couple that is sitting on the fence about getting married.  But
 Jalon, Phoebe, Malachi, and Blue still have cameos in the book!
Leanna and Roman are both odd ducks.  Leanna is a bit of a tomboy and
 is not good at what women in Amish society are expected to do (i.e., 
cooking).  She works for Daniel, who (if I recall correctly) is a 
carpenter, and a couple of busy-bodies are spreading rumors that she and
 Daniel are having an affair.  Daniel fires her, and she initially 
thinks it was because she read a note that she was not supposed to read.
Roman is a creative person, one who excels at coming up with ideas 
and drawing technical designs.  He does not have a whole lot of 
discipline with hands-on work, though.  Years before, he left the 
community.  His dream is to get a degree at a college, and he wrote the 
college a letter.  Because he left, he and Daniel are estranged from 
each other.  When he learns that his grandmother has died, he returns 
home, as his grandmother encouraged him to become reconciled with his 
brother.  We learn in the course of the book that their parents were 
rather cold and did not show affection.
Other things happen in the course of the book.  Daniel is injured.  
Barbara is pregnant and loses the baby.  Karen and Adam are each waiting
 for the other to make the first move.
I read this book over the course of two months, a little each day.  
It was an enjoyable book.  Roman does a lot of growing up, and Leanna 
gets to observe this because she was acquainted with him before he 
left.  Roman and Leanna were also characters for whom I wanted to root, 
as they were underdogs, in a sense.  The book had enough going on that 
it was not boring.  And its ending set the stage for the next book of 
the series.