What I can presume is that this book is sort of an epilogue of a very intense and troubled relationship between the two women protagonist in the second world war period with all its atrocities. And from what I can guess, in the previous books our heroines had their personal stories laced in such barbarities but also graced with great acts of courage, love and patriotism.
Eva and Zoe have an incredible love forged through unspeakable events that only in this last book the details from behind the scenes emerge. This book comes through to me as the volume that brings healing to wounds both physical and physiological, individual and family wise and as a fresh start to many questions that were left unanswered.
So I would suggest to read the previous books if you would like to enjoy to the full the dramatic plot that unfolds in a very heart rendering saga.