In To Your Scattered Bodies Go, Philip José Farmer introduces readers to the awesome Riverworld, a planet that had been carved into one large river on whose shores all of humanity throughout the ages has seemingly been resurrected. In The Fabulous Riverboat, Farmer tells the tale of one person whose is uniquely suited to find the river's headwaters, riverboat captain and famous Earthly author Sam Clemens (a.k.a. Mark Twain). Clemens has been visited by "X," a mysterious being who claims to be a rebel among the group that created Riverworld. X tells Clemens where he can find a large deposit of iron and other materials that Clemens can use to build the greatest riverboat ever seen. Since there is virtually no metal on the planet, it will also give Clemens an unbeatable edge when it comes to battling the various warlike societies that dominate the Riverworld.
But Clemens is not alone in his quest for the iron, which arrives on the planet in the form of a giant meteorite. In fact, Clemens is besieged on all sides by forces determined to seize the precious ore, leading him to make a deadly pact with one of history's most notorious villains, John Lackland. Lackland's crimes during his reign as king of England were so hideous that no other English monarch will ever carry his name, and he's up to equally nefarious tricks on Riverworld. However, Clemens has a guardian angel in the form of Joe Miller, a giant subhuman with a big nose, a serious lisp, and a cutting wit. Miller has also been to the very headwaters of the river, where he saw a mysterious tower in the middle of the North Sea and where the creators of Riverworld are thought to reside. He will be an invaluable ally in completing the riverboat and sailing to the headwaters, but even an 800-pound giant may not be enough to help Clemens fulfill X's mission.