The artefact in question is called the Mirror of Smoke. Two thousand years ago a battle was  being fought over the relic. Totec was the leader of the Army of Light, his side won and he took control over the mirror. He banished Xolotl and became the Guardian of Light. Totec entombed himself in the mirror within the Temple of Light to keep it from falling into the wrong hands. Two thousand years later, Lara Croft discovers the mirror in a temple deep within the jungles of Central America. Lara Croft is then ambushed by a group of mercenaries who steals the mirror. They had apparently been following Lara's move. With the mirror removed from the Temple of Light (wait...Isn't that a Zelda game?), Xolotl returns to power, kills the mercenaries, and vanishes. Totec returns and decides to blame Lara for her recklessness, but realizing that they must work together to get back the Mirror of Smoke.