I read in a physics book that given the spin momentum is high the torque will turn the spin angular momentum instead of making the pendulum fall. What law governs this??
Actually - if you start from rest, the gyroscope does fall. A tiny little bit. And it is that initial downward motion that leads to the forces needed to start the precession. The downward motion leads to a torque about the vertical axis, and starts the precession. The motion is called nutation; with time, this up-and-down motion is usually damped out and you end up with pure precession (at an angle slightly below the vertical; that's how you maintain the zero angular momentum about the vertical axis).
The laws that apply are still the same Newton's laws... equilibrium only exists when the gyroscope is precessing, and the mechanism described in the link explains how that precession starts.