Think of a NumberBy: John Verdon It begins with a letter . . . The letter contains a request think of a number, any number and a sealed envelope. And inside the envelope is that number. When Dave Gurney, retired NYPD homicide detective, is contacted by an old college acquaintance about some startling letters he's been receiving, he thinks it's little more than a diverting but sinister puzzle. That is, until the acquaintance is brutally killed. Suddenly Gurney finds