In the third volume, The Dark Design, Clemens finishes his second boat after many hardships and attempts by others to steal this one, too. After he leaves, another group at the base builds a dirigible and flies it to the tower. Only one of the crew can get inside the tower, and he does not come back out. On the way back, one of the crew is discovered to be X, but he escapes, and the airship is blown up by a bomb he planted.
In the fourth volume, The Magic Labyrinth, the two heavily armed riverboats meet. Both are sunk in the battle, and their captains die along with most of their crews. Burton and some of X’s recruits survive. They go up The River as far as they can in a small boat, then climb the massive and rugged mountain range ringing the north polar sea. Burton is convinced that one of the party is X. After the party gets into the tower through an entrance secretly installed by X, Burton does find out who X is.
However, in the long absence of all its Ethical and Agent tenants (slain by X), the unattended tower mechanisms need some maintenance. Not getting it, a valve that admits seawater is stuck, and the protein brain of the Computer is threatened. If it dies before the valve can be repaired, the entire project will be doomed, and all the body-recordings will perish.
Hermann Goring, ex-Nazi and late Reichsmarschall of the Third Reich, is one of the party. He has repented his evil deeds on Earth and has converted to the Church of the Second Chance. He sacrifices his life trying to get to the malfunctioning valve to repair it. He fails, and it seems that the Computer will perish and with it all hope of immortality for the thirty-five billion people.
However, Alice Liddell Hargreaves, one of the party, ingeniously figures out a way to circumvent the Computer’s suicidal obedience to certain inhibitions, and the project is saved.
Now the Valleydwellers will be given the extra time that Loga, the renegade Ethical, claims they need in order for all to attain the level where they may Go On. The project will be resumed as originally planned with this exception. Loga’s fellow Ethicals and their Agents will not be resurrected because they would interfere with his plans.
The book at hand, Gods of Riverworld, starts a few weeks after the ending of the fourth, The Magic Labyrinth.