Star Wars: Thrawn Ascendancy: (Book 3: Lesser Evil)

Thrawn and his allies race to save the Chiss Ascendancy from an unseen enemy in the second book in the epic Star Wars: Thrawn Ascendancy trilogy from bestselling author Timothy Zahn.
Thrawn's latest triumph still rests newly on his shoulders. Despite leading the Chiss to victory and bringing glory to the House of Mitth, the true threat to the Ascendancy has not yet been extinguished. Their foes do not send threats or ultimatums, or mass ships on the edge of the Chaos. Their weapons come cloaked in smiles and generosity: Gifts offered freely. Services granted unconditionally.
Across the Ascendancy, seemingly inconsequential events could herald the doom of the Chiss. As Thrawn and the Expansionary Defense Fleet rally to uncover the enemy plot, they discover a chilling truth: rather than invade Chiss capitals or pillage their resources, they strike at the very foundation of the Ascendancy, seeking to widen the rifts between The Nine Ruling Families and the Forty Great Houses below. As rivalry and suspicion sow discord among allies, each warrior must decide what matters most to them: the security of their family, or the survival of the Ascendancy itself.