GM   September 1st   The Ministry of Powers, London   There were, of course, a number of government agents. Armed ones, too. And a number of bustling, virtually faceless civil servants. But the only two men with any gravity in the plush office, decorated in oak, with lined leather volumes gilding every wall were the Minister for Powers, the Rt Hon. Cecil Booth, and Sir Cruxberry, who actually ran the agency.    Cecil Booth was middle aged, slightly rounding, and moderately intelligent. A