William Samuel Stephenson, businessman, inventor, amateur boxing champion, World War One flying ace, is a hero whose story has been more than twenty years in the telling. A millionaire before he was 30, Sir William found his international business interests are ideal ""cover"" for intelligence operations in anticipation of World War II. When the time came to choose a director for British Security Co-ordination (the element designed to protect England's war-supply effort in America and to conduct intelligence operations in cooperation with America's Office of Strategic Services) Sir William was an inspired, as well as a logical, choice for the post. Hyde, who was a member of B.S.C., admires his former chief's unobtrusive personality so much (the book's title in England is The Quiet Canadian) that he has chosen to tell Sir William's story largely by means of the events connected with B.S.C.'s operations: the liaison between B.S.C., the F.B.I., and General Donovan's O.S.S., the incredibly complicated schemes for financing the work of special agents, the wrangles over the inviolability of files, the actual interception of enemy spies, including those of the Gouzenko affair. Sidelights on the Roosevelt Administration, Roosevelt himself, J. Edgar Hoover, Donovan, Drew Pearson -- whose provocative prewar newspaper columns excited interventionist alarm and ire -- and many other figures of the day make this as much an American book as an English one. It has as much (or more) cloak-and-dagger as Robert Alcorn's recent No Bugles for Spies (McKay, p. 870, 1962), and is enhanced by an unusual sensitivity to the subject.