Nobody knows the crooked turns, slippery slopes, and dark, dangerous stretches of the Beltway better than Margaret Truman, dean of the Washington, D.C., mystery scene. And no one is better equipped to lead a suspenseful tour into the treacherous territory of big-time political lobbying, where the right information and enough influence can buy power-the kind that corrupts . . . and sometimes kills. Arriving home from a fund-raising dinner, senior...