Gar Nal is a rival of Fal Sivas, another Zodangan inventor. At the start of the story, both inventors have been working for years on spaceships capable of interplanetary travel (something that has not been achieved yet upon Barsoom). They frequently spy on each other and steal each others ideas whenever possible. At the start of the story the rivalry between the two has risen to such great proportions, that Gar Nal hires Ur Jan, the leader of the Zodangan assassins guild, to kill Fal Sivas. John Carter, who is on a mission in Zodanga to defeat the guild, responds to this by becomming Fal Sivas' bodyguard.
When Gar Nal and Ur Jan realize they are dealing with the Warlord of Barsoom, they conspire to abduct Dejah Thoris and use Gar Nal's ship to take her to Thuria. They succees in their plan, but once on Thuria they are promptly taken captive by the Tarids. When John Carter, Zanda and Jat Or follow them to Thuria in Fal Sivas' space ship, they too are captured. The two groups form an uneasy alliance to escape their mutunal enemies. During the escape attempt, Gar Nal double crosses John Carter and abducts Dejah Thoris again in his own ship, leaving Ur Jan behind. Enraged by this betrayal, Ur Jan swears loyalty to John Carter.
After John Carter returns the woman Ozara to her people and is reunited with his allies, he learns that Gar Nal and Dejah Thoris are apparently prisoners in a rivaling country named Ombra, but before Carter can go there Fal Sivas causes his ship to return to Barsoom. On Barsoom Carter soon learns that Gar Nal had escaped his captors and also returned to the planet. He and Fal Sivas have now formed an uneasy truce; Gar Nal will hide Fal Sivas from John Carter in return for Fal Sivas' secret of the mechanical brain that pilots his ship. John Carter soon finds and confronts both men in Gar Nal's house. In a last attempt to save himself, Gar Nal lies that Dejah Thoris is still in Ombra, hoping that John Carter will go back there to save her. In reality she is tied up in the next room. She manages to free herself and expose the lie just in time, after which Ur Jan kills Gar Nal.