‘Retaliation,’ the third book in the ‘Sentinels of Tzurac’ sci-fi trilogy, is the action-packed finale, where the forces of good and evil struggle for the control of the Universe through possession of the powerful resource Xytrinium.  Some of the characters which the readers loved or loathed from the previous two books reappear with more determination to succeed. Surprisingly, an unexpected hero, trying to redeem himself and clear his conscience from his past foolish mistakes, emerges in an attempt to help thwart the...