The best description I've seen of Elizabeth is missing by Emma Healey is 'unsettling'. Not because of the mystery surrounding the missing Elizabeth, or the mystery of the disappearance of Sukey, sister of Maud (the main character), but because of the way the author imagines how it is to live with dementia and have fluctuating memory capacity. Maud is an extremely sympathetic character but at the same time is infuriating, spiteful and tiresome, especially for her loving but long-suffering daughter. Dementia as depicted in this novel - and who knows how realistic it is - is a truly terrible illness.
I think this is definitely a book worth reading and it would be good for a book group (although it's not on either of my book club lists currently - I need to crack on with books I'm actually supposed to be reading).