Kate and Zoe met at 19 when they both made the cut for the national training program in track cycling --- a sport that demands intense focus, blinding exertion, and unwavering commitment. They are built to exploit the barest physical and psychological edge over equally skilled rivals, all of whom are fighting for the last one-tenth of a second that separates triumph from despair.

Now at 32, the women are facing their last and biggest race: the 2012 Olympics. Each wants desperately to win gold, and each has more than a medal to lose.