Diving in mini-subs off the coast of North Carolina with famed treasure hunter Bill Robinson, the BION team digs up a shield belonging to the ancient order of the Knights of the Crusades. When a rival group of treasure hunters plots to take the Knight's treasure for themselves, Bill winds up in the hospital when his oxygen tanks fail, and a planted chest of fake gold coins causes the BION team to be accused of fraud. Returning to the dive site, Bill and the BION team discover the rival group is searching for the Holy Grail! Rip gets his hands on the grail, only to have it drop down an abyss! While Sam leads the treasure hunters away in a wild goose chase of mini-subs, Rip descends deeper into the abyss, only to give up when his equipment cracks under intense pressure. Did Rip have his hands on the world's most famous artifact? Believe it or Not!