Sorry, late response…watching the 'lympics!
The original book is on ISBN Ref 075382566X – Valkyrie: The Plot to Kill Hitler by Philipp von Boeselager.
PvB encouraged by his daughter to break silence – not a novel, more like a chronological memories, interesting values from his childhood brought up in the great outdoors – spent years as a cavalry officer, looked after his men and his horses.
Not written in a big hollywood way, more humble if you ask me. I enjoyed the read.
How did the film go?