Enemies of the Heart by Rebecca Dean

Second Hand 

A sweeping epic of love, desire and betrayal. The perfect read for fans of THE CROWN.

June 1909, in a large Berlin mansion, cousins Zelda and Vicky are about to meet brothers Berthold and Josef for the first time - an evening that will alter the course of their lives forever...

Vicky Hudson is only seventeen when she marries Berthold and moves from her idyllic Yorkshire home to Berlin. She finds it hard to adjust to her new life, not least when she discovers that the family business she has just married into - Remer Steel - is producing weaponry for the German army. With the First World War looming, Vicky flees to Yorkshire with her children, leaving Berlin, and her husband, behind.