In Helen MacInnes's novels—"Cloak of Darkness" is her 20th—every cafe and konditorei in Europe is a launching pad for terrorist activity, funded, encouraged and often directly organized by that source of all global evil, the K.G.B. The hand that brushes the Sacher torte crumbs off a lapel may shortly be carrying a Russian grenade. For many years Miss MacInnes has been the Claire Sterling of fiction; not even détente thawed her cold-war message. In "Prelude to Terror" (1978), the heroine, a Western agent, summed up the prevailing attitude: "There's a job to be done, a necessary job. Someone has to do it; we can't all sit back and watch the totalitarians take over." She goes on, "I know it has to be done. Or else we'll all end up regimented nonentities, scared to death to step out of line or raise our voices. Everything...