Ahh, it's years since I've read Agatha Christie, but it's like putting on a pair of my favourite comfy slippers; I know exactly what to expect.
Big country house - check
Dysfunctional family - check
Missing/disputed will - check
Suspicious servants - check
Red herrings galore - check
Everyone has a motive - check and check
Luckily Hercule Poirot is available and I'm sure he'll have everything sorted out and the murderer exposed in time for afternoon tea.