A Plague of All Cowards (1976) by William Barton

Starover Series, Book 3: A Plague of All Cowards

Originally published in 1976 by Ace Books, A Plague of All Cowards sends space mercenary (and former war criminal) Zoltan Tharkie on a galactic quest to capture a dangerous assassin and unmask his hidden masters. Includes the revised ending discarded by the original editors which foreshadowed much of Barton's later work, along with a discussion of the history and evolution of the Starover Universe.