When last we saw the book of destiny, it had been buried in the American west of the mid-1800s. But it couldn't stay buried. Edward Conqueror, a British explorer most likely based on Professor Challenger from Arthur Conan Doyle's novel The Lost World, discovered the book when excavating a Native American burial ground, as his descendant testified about at the Youngblood murder trial.
Edward Challenger and family went missing and nothing was heard of them for years.
Ten years later Prophet would bring the book with him on a Doc Savage-inspired adventure where he passed on the book to the WWI flying ace, the Phantom Aviator:
It's starting to become clear how Moore is creating a shared universe of almost every kind of boys adventure genres in comics, from lost worlds with dinosaurs to Tarzan-inspired jungles to WWI flying pilots and 1930s noir heroes, such as The Fog. Moore would go on to repeat this trick in the League of Extraordinary Gentlemen, but this is a fascinating warm up.
Anyway, the Phantom Aviator would fly again in WWII, where we'll see the book next.