Shadow Lord — Laurence Yep

Angira is a primitive planet -- and young Prince Vikrram returns from Earth filled with new ideas. When Sulu and Spock accompany Vikram home, they walk into a bloodbath: reactionary forces, afraid of any modernization, have seized Vikram's rightful throne. Suddenly the men from the Enterprise are on an underground journey with a Prince who is coming of age. The future of Angira is at stake, and each man's survival depends on his skill--and daring--with a sword!