Mirror in the Sky (Berkley, X1743)

160 pp. "Ultimate war on an alien planet--but who was the enemy? The Creeps--mysterious aliens locked in a death struggle with the human race...diabolically clever in their ability to mimic human devices and tactics. The war between the Creeps and the men of Earth had lasted for years--a war so savage and bitter that human combatants were issued a daily drug ration to keep them sane. But one soldier was immune to the drug--and learned the unspeakable secret of the Creeps...and of the war!"