Swords of Mars

Swords of Mars was published in 1936 and brings John Carter himself back to the center of the action after several novels focusing on other characters. Carter, in his role as Warlord of Barsoom, is investigating the powerful Assassins Guild of Zodanga, which has been systematically eliminating his political allies across the planet. He infiltrates the guild under an assumed identity and ends up traveling on a flight to Thuria, the closer of the two Martian moons, where the guild's leader Ur Jan has established a base.

The Thuria sections are unusual in the Barsoom canon for taking the action off the surface of Mars entirely and into a new lunar environment with its own ecosystems and political structures. There is a memorable subplot involving an automated robotic spaceship, one of the earliest depictions of artificial intelligence pilot systems in pulp fiction. The book is shorter and tighter than some of the later Barsoom novels, with a clear adventure arc and a satisfying resolution. A return to the John Carter formula that fans had been asking for.