All My Enemies — Rosemary Harris

Jenny Emerson had waited for years for this moment, when her long-lost twin sister Elizabeth would at last reenter her life. Kidnapped at thirteen, Elizabeth had vanished so utterly that Jenny had gained a successful career, a charming husband, and a beautiful little daughter. And now Elizabeth was to return and make her joy complete. The great event occured -- but something was wrong from the start. Jenny watched with growing terror as her happy, comfortable world came apart, as hatred and violence drove her into a life-and-death chase from London to Paris to the dun-drenched, teeming bazaars of Alexandria....