Elsewhere on Barsoom, the Red Martian cities of Helium and Zodanga have been at war for a thousand years. Sab Than, Jeddak of Zodanga, armed with a special weapon obtained from the Thern leader Matai Shang, proposes a cease-fire and an end to the war by marrying the Princess of Helium, Dejah Thoris. The Princess escapes and is rescued by Carter. Carter, Dejah, and Tarkas' daughter Sola, embark on a quest to get to the end of a sacred river to find a way for Carter to get back home. They obtain information about the "ninth ray", a means of using infinite energy and also the key to understanding how the medallion works, but are attacked by Shang's minions, the Green Martians of Warhoon. After the attack, Carter is captured and taken back with Dejah while Sola is able to escape. The demoralized Dejah grudgingly agrees to marry Sab Than, then gives Carter his medallion and tells him to return to Earth. Carter decides to stay and is captured by Shang, who explains to him the purpose of Therns and how they manipulate the civilizations of different worlds to their doom, feeding off the planet's resources in the process. Carter is able to make an escape as he and Sola go back to the Tharks requesting their help. There they discover Tarkas has been overthrown by a ruthless brute, Tal Hajus. Tarkas, Carter and Sola are put on trial in a colosseum battle with two enormous vicious creatures, the four-armed Great White-Apes. After defeating them and killing Hajus, Carter becomes the leader of the Tharks.