Assegai - Wilbur A. Smith

It is 1913 and ex-soldier turned professional big game hunter, Leon Courtney, is in British East Africa guiding rich and powerful men from America and Europe on safaris in the Masai tribe territories. One of his clients, German industrialist Count Otto von Meerbach, has a company which builds aircraft and vehicles for the Kaiser's burgeoning army. But Leon had not bargained for falling passionately in love with Eva, the Count's beautiful and enigmatic mistress.
Just prior to the outbreak of World War I, Leon is recruited by his uncle, Penrod Ballantyne, Commander of the British Forces in East Africa, to gather information from von Meerbach. He stumbles on a plot against the British involving the disenchanted survivors of the Boer War, but it is only when Eva and von Meerbach return to Africa that Leon finds out who and what is really behind the conspiracy.

'A Rider Haggard for our times' Financial Times