On assignment in the Middle East, television journalist Cotten Stone stumbles upon an archeological dig that uncovers the world's most-sought-after religious relic: the Holy Grail. With his last dying breath, Dr. Gabriel Archer gives it to Cotten, uttering "You are the only one" in a language she's heard from only one other person--her deceased twin sister.

What begins as a hot news story for the ambitious young reporter soon turns into a nightmare when the Holy Grail is stolen and strange "accidents" befall her dearest friends. Running for her life, she turns to John Tyler, a priest with firsthand knowledge of religious artifacts, for help. An anonymous source leads them to New Orleans during Mardi Gras, where an abominable experiment is underway that--unless destroyed--promises to unleash an ancient evil upon the Earth.