This is supposed to be the book that inspired the producers of the hit BBC series, Downtown Abbey. I can see the connection. It's not the exact same storyline, but it's the same locale and era - Titanic sinking, World War I, prohibition, flappers, landed gentry, being in service, shell-shock, laws of primogeniture, sister relationships - and it's a great read!!
The twists and turns are gripping. You really don't have it all figured out until the very last page.
Don't start unless you have time to finish - or all your chores and obligations will go undone until you do finish!