Superman. Wonder Woman. The Flash. Power Girl. The Doom Patrol. Hawkman. Aquaman. The Teen Titans. They're among the mightiest beings who have ever lived. Together, they are a force that can vanquish any known threat to the universe-But what about the unknown? When a mysterious being called Megistus travels between centuries to steal objects and abduct people, it'll take all of DC's heroes and the Challengers of the Unknown, who possess the Book of Destiny, to thwart this evil threat!