This was the third and much the best of the Rex Carver series of thrillers that Victor Canning wrote in the 1960s. See also
The Whip Hand (Arcturus Crime Classics) and
Doubled in Diamonds. Our hero is engaged to recover some stolen property, and pursues the thief to France, Italy, Libya and eventually Ibiza, getting himself tortured by the British Secret Services en route, and getting help from his secretary Hilda Wilkins and her Suez Canal pilot fiance. Very readable but far-fetched, of course. Or was it so far-fetched, considering that Canning manages to predict a spy exchange that actually took place two years after publication?