A Christmas Thriller focused on an excessively rich American family. They have crazy traditions and a shroud of secrecy around them. 

When Harriet, a British Thriller Author, newly engaged gets thrown into meeting her future in-laws it is quite overwhelming. The Holbeck's have an American dynasty and she's an orphan. 
A tape from the pariarch Robert Holbeck, the first time she met him changes everything.

It feels cinematic. The audiobook performance (by the author!) and sound design are fantastic. I loved that the tapes had the sound and texture of an anologue recording.