GILES MILTON HAS a gift for searching out odd and forgotten corners of history and turning them into best- selling books. Nathaniel’s Nutmeg, which dealt with the spice trade, has sold over half a million copies to date, and it is easy to see his new book doing as well. For this is not a dry history, but a full-blooded narrative closer in style to a historical novel than to an academic study. The chapter headings sound like a run of Technicolor movies from the 1950s: ‘Sultan of Slaves’; ‘Seized at Sea’; ‘Blood Rivals’. One can almost see Virginia Mayo’s bosom heaving.