The Key to Rebecca — Ken Follett

He is known to the Germans as 'Sphinx', to others as Alex Wolff, a European businessman. He arrives suddenly in Cairo from out of the desert, armed with a radio set,
a lethal blade and a copy of Daphne du Maurier's REBECCA - a ruthless man with a burning, relentless conviction that he will win at all costs.

The stakes are high, for the survival of the British campaign in North Africa is in the balance. Only Major William Vandam, an Intelligence officer, and the beautiful courtesan, Elene, can put an end to Wolff's brilliant clandestine reports of British troop movements and strategic plans...

In this desperate race against time, as Tobruk falls to the Panzer divisions and the sky of Cairo is blackened with fragments of hastily burned security documents, Vandam and Wolff become locked in a deathly struggle which will determine who wins - and who loses - the greatest war the world has ever known...