Shadow Lord

Summary
From the back cover: Angira is a primitive, violent planet - and young Prince Vikram 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 rightul 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!