The Fearful Summons

Summary
From the back cover: Captain Sulu of the U.S.S. Excelsior and his crew are kidnapped. When Federation-conducted negotiations come to a standstill, Captain James T. Kirk and the former officers of the U.S.S. Enterprise reunite to rescue their old comrade.

The officers learn carrying out their mission could prove difficult when the encounter the kidnappers - a greedy, little-known race called the Thraxians, who believe their way is the only way. Now the Thraxians are demanding super-powerful weapons in exchange for the hostages.

With no other alternatives, Kirk is forced to consider giving in to the Thraxians to save the Excelsior crew - a decision that could save a few, but endanger the lives of an entire star system…