Historical fiction/mystery book recommendations that aren’t depressing

My moms birthday is coming up and I want to get her a book. She likes historical fictions and mysteries but not ones that are super depressing. She loves learning fascinating facts about history or psychology, so more of a historical fiction with those themes and ones less focused on super sad events and deep trauma that characters go through. She also finds history about the royals super interesting, for example she loved watching The Crown. My mom also gets board easily so preferably recommendations for books that don’t drag on too long.

Thanks!

by Electronic-Fan7077