The Clockwork Traitor. Family d'Alembert Book 3

Jules and Yvette d'Alembert had faced challenges before - but rarely one as daunting as this. To them fell the perilous task of infiltrating a vicious conspiracy which threatened to destroy the Stanley dynasty and throw the whole of interstellar civilisation into chaos. Now, as rival candidates from all corners of the galaxy gather for the Progress, the two most daring space super-agents of all time go into action.
For among the suitors competing to be consort to the royal heiress of the Empire of Earth, there is a traitor. And somewhere close to the Princess, a time bomb is ticking...