The Catch by Alison Fairbrother

 Ellie's beloved father, Jim, dies early in the book (so I'm not spoiling any plots). She is devastated at losing him and even more devastated when his will is read. Jim had gone through multiple wives and had multiple children with said wives and he left each of the other offspring something of sentimental importance to them. Ellie always assumed she was his favorite, so she thought she'd get his most prized possession--a baseball. Instead, she gets a gingerbread tie rack--and the baseball goes to a mystery person named LM Wright.

After the funeral, she goes back to her jobs as a writer for an online magazine in DC--and her affair with a married man, Lucas (whom her father, ironically enough, didn't approve of). She sets out to find the mysterious LM Wright and in the process learns a lot about her father (not all of it flattering) and herself.