Better than Moby Dick?: Yes
The conflict between Mersia and the Terran Empire is a primary focus of all Poul Anderson's Technic series books. The Day of Their Return is no different. Commissioner Chunderban Desai is sent to the frontier planet Aeneas, to restore order after a recent insurrection. The recalcitrant Aeneans still desire independence. The Terran Empire is afraid the Mersians will try to use Aeneas to drive a wedge into the Empire and hasten the beginning of the Long Night.
The seeds of rebellion are still strong on Aeneas. Young Ivar Frederikson, Firstman of Ilion, stirs the people's hearts when he attempts an attack on a Terran patrol. The attack fails and Ivar is forced into hiding; Commissioner Desai tries to bring him to justice, but is constrained because he fears to create a martyr.
While Ivar hides out among various nomadic groups, strange things are going on elsewhere. Aycharaych, a mind-reading Mersian agent, is loose on Aeneas. An Ythrian agent is also operating on Aeneas--and Ivar hopes to secure Ythrian aid for the Aenean independence movement. Finally, the prophet Jaan claims that the fabled Elder Race--which built the ancient ruins on Aeneas--will shortly return and free the people.
Minor spoiler: the nomadic tinerans of Aeneas keep pets which they call lucks, and which the Ythrians call slinkers. Unbeknownst to the tinerans, the slinkers are emotional amplifiers, reflecting emotions back at those around them.
The Day of Their Return to be one of Anderson's better books. It rates a strong 3. I wanted to give it a 4, but Anderson doesn't follow up on the slinkers--they're a throwaway plot element.