Title: The Clockwork Traitor
Description: From back cover of Jove/HBJ paperback March 1979:

TREASON THREATENS THE GALAXY

A robber captured in far-off Kolokov knows a secret that threatens the stability of the succession of the Throne of the Empire of Earth.  But he withstands the powers of the fatal truth-telling drug nitrobarb and dies before revealing the traitors' names.  Daring secret agents Jules and Yvette D'Alembert, possessed of lightning reflexes and super-strength, are faced with a far-reaching and baffling plot.  They join forces with the rest of the D'Alemberts to uncover the "time bomb" that menaces the Princess' life and the control of the Galaxy's most populated sector, Earth!
Subjects: Fiction in English