Rainmaker by Sandra Brown

In a break from her more typical mysteries, Brown tells a tale of Depression era Texas.  David Rainwater takes a room in a boarding house run by a Ella Barron.  Ella, whose husband has abandoned her,  desperately protects her young son Solly whose odd behavior we would identify today as autistic.  David finds a way into Solly's world.  A single event and a choice that Rainwater makes, changes their lives.  There are other quirky characters in the town but all were believable and worthy of a happy ending. The ending, by the way, was a surprise to me but you may figure it out earlier.