Dwellers in the Crucible (Star Trek #25)

DWELLERS IN THE CRUCIBLE Warrantors of Peace: the Federation’s daring experiment to prevent war among its members. each Warrantor, man or woman is hostage for the government of his native world — and is instantly killed if that world breaks the peace. Now Romulans have kidnapped six Warrantors, to foment political chaos — and then civil war — within the Federation. Captain Kirk must send Sulu to infiltrate Romulan territory, find the hostages, and bring them back alive — before the Federation self-destructs