While Gabriel is protecting the infant heir of an English Prince from "the night visitors", the baby is kidnapped right out from under his nose. Gabriel trails the kidnappers to a small town in France called Rennes-le-chateau, which is the site of an ancient mystery involving a buried treasure rumored to be the holy grail. Strangely enough, his old friend Mosely is also in Rennes-le-chateau on a "treasure-hunting tour". And of course, in classic mystery fashion, every member of the tour group has his or her own secrets, casting them all in a cloud of suspicion. Things really heat up when Gabriel's assistant/partner Grace arrives, and, similar to GK2, the player alternates between playing each of the main characters in a race to solve the mystery of Rennes-le-chateau and find the missing child.