The Warlord of Mars by Edgar Rice Burroughs

They go to Marentina, a nearly inaccessible glass-domed city, a hothouse of sorts in the arctic. Talu tells them that Helium's 'ruler and his company' are captives of Salensus Oll, Talu's uncle, with whom he is at war. Here Carter and Thuvan Dihn save Talu, prince of Marentina, from assasination. The chase now takes them to the North Pole, to the hidden city of the Okar. Carter follows close behind, along with Woola and Thuvan Dihn. Matai Shang and Thurid are forced to flee again with their prisoners, now going north. Carter tells Kulan Tith that Matai Shang is holding both Dejah Thoris and Thuvia prisoner at Kaol. Kulan Tith, still a true believer, banishes Carter from Kaol forever and tells Thuvan Dihn to settle his differences with Matai Shang, the Father of Therns, elsewhere. Fortunately for him, Thuvan Dihn, Jeddak of Ptarth, is also there, and he can testify that Carter is on their side and saved his daughter Thuvia. He makes it into the palace of the jeddak, Kulan Tith. Disguised as a Red Martian Carter also enters the city. Thurid and Matai Shang first flee to Kaol, where the religion of Issus is still holding strong. Thus begins a quest by John Carter to liberate his beloved wife. He cannot, however, prevent Dejah Thoris, Thuvia, and Phaidor from being carried away by Matai Shang, Thurid and other Therns. Carter and Woola follow them when they enter an underground river, which leads to a secret tunnel to the Temple of the Sun. When he follows a mysterious figure beside the Lost Sea of Korus, he discovers that the First Born Thurid and the Thern Matai Shang have joined forces to get revenge at Carter for exposing their religion as a fraud. Six months have passed since the previous book, and John Carter is still searching for an alternative way to get Dejah Thoris out of the Temple of the Sun. It is said one has to wait an entire Barsoomian year before the room the prisoner is in revolves back to the entrance.

At the end of the previous book, John Carter's wife, the princess Dejah Thoris, is imprisoned in the Temple of the Sun by the vile pretender goddess Issus. This novel continues where the previous one in the series, The Gods of Mars abruptly ended.

The Warlord of Mars by Edgar Rice Burroughs