Welcome to the Pepsi Generation. As Pepsi fires up a hot new ad campaign, Coca-Cola starts getting nervous. But a sudden plane detour through Ireland gives Coke executive Bill Backer inspiration for one of the most iconic ads of the 20th century. It seems Coke is on top once again—but Pepsi has another trick up its sleeve. The company is out for blood with the Pepsi Challenge, a nationwide taste test that will endanger the most precious part of Coca-Cola lore: its secret recipe.