The Map of Love by Ahdaf Soueif
In 1900 Lady Anna Winterbourne travels to Egypt where she falls in love with Sharif, and Egyptian Nationalist utterly committed to his country's cause. A hundred years later, Isabel Parkman, an American divorcee and a descendant of Anna and Sharif, goes to Egypt, taking with her an old family trunk, inside which are found notebooks and journals which reveal Anna and Sharif's secret.