Obsidian Fate — Diana G. Gallagher

ETERNAL NIGHT

On the outskirts of Sunnydale, recent rains have uncovered the remains of a five hundred-year-old Spanish expedition. But one of the artifacts, a smoky mirror with an ornately carved obsidian frame, goes missing, along with the history teacher who found it. And when Buffy narrowly escapes the attack of a black jaguar while on patrol, Giles puts the gang into research mode.

An ancient volume identifies the missing mirror as a magical object formed by the Aztec god of darkness. A mortal who looks into the mirror will see his or her fate -- and can be manipulated by the evil god, who is scheming to regain his power. Taking their destinies into their own hands, the Slayer and her friends rush into a ferocious battle between light and darkness in the shadows of a massive Aztec temple, a battle against perpetual night -- and the evil that thrives in the dark hours.