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A dozen sentient species occupy the galaxy, and the Quadrail connects them all. Arriving at Proteus Station under a cloud of suspicion, ex-government agent Frank Compton finds he must answer for the death of six members of the Filly elite, a crime for which he has been falsely accused. Filiaelian captivity, however, is the least of Compton's worries, for his horse-faced alien accusers are guarding a terrible secret that dates back centuries: the Shonkla-raa, a race of super-soldiers believed to be extinct.

Invincible fighters bred for conquest and dedicated to the destruction of the Quadrail, as well as the annihilation of the unsuspecting billions who oppose them, the Shonkla-raa must be stopped at all cost. But to do so, Compton and his beautiful, enigmatic half-human partner, Bayta, will have to ally themselves with the insidious, mind-enslaving Mohdri, the malevolent group intelligence they have sworn to destroy.

Hugo Award winner Timothy Zahn concludes his sensational Quadrail series with a riveting futuristic adventure that combines the best of three popular genres—hard science fiction, mystery, and espionage thriller. Judgment at Proteus is a breathtaking tale of deception, murder, and desperate maneuverings in a secret war that threatens the survival of every living being in the galaxy.

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Release date

Audiobook: 13 May 2025