Eric Marsh is part of a scientific expedition in Burma, c. 1902, in search of the legendary city of Alaozar, to be found on the Plateau of Sung. Things haven't been going easily, especially since the natives are reluctant to provide guides, due to fear of the "Tcho-Tcho People" said to live on "The Lake of Dread." In proper early 20th century style, the explorers have dismissed their fears and soldiered on.
Marsh has to break ranks and briefly return to the camp they've left behind because he didn't remember to pack all his stuff. This happens to save him as when he's riding back to join his group, he hears screaming and, hiding in some bushes as he realizes he can't do anything to stop it, he watches them get slaughtered by a group of pygmies that are identified as the Tcho-Tchos.
With his team dead, Marsh decides there's no point in going back, so instead he rifles the bodies (the Tcho-Tchos took all the tools and weapons but left the food and water, and since they took the shovels, he cannot bury the bodies) and sets off to find the lost city alone. He does briefly stop to consider what's just happened with "grief mingled with fear". He makes his way within sight of the city itself, which isn't too difficult since the city is shooting beams of white light into the sky. Marsh settles down to make camp but is jumped by Tcho-Tchos and wakes up in a bed in Alaozar. He's greeted by Dr. Fo-Lan, a Chinese scientist who was thought to have died some years ago. Instead Fo-Lan has been a slave of the Tcho-Tchos all this time, forced to help them unleash some awful terror upon the world. Fo-Lan tells Marsh that now, the two of them can thwart the Tcho Tchos' sinister plans.
Fo-Lan leads him down a secret passage, where they watch the Tcho-Tchos bow down to their leader, the priest E-Poh ("he is seven thousand years old" says Fo-Lan), and the tentacle-lump monster that lurks in the shadows, which Fo-Lan informs him is named Lloigor. Fo-Lan asks Marsh to watch his body while he astrally projects to get help. This goes off without a hitch. Once back in flesh, Fo-Lan informs him that he must convince E-Poh to open the gates to Zhar and Lloigor, at which time "the Star Warriors" can come and save them.
Fo-Lan goes to E-Poh and tells him that Zhar says the Tcho-Tchos must summon Lloigor and Zhar from the city, while he and Marsh go out onto the plateau and do a ritual of their own. Despite displaying incredulity that Zhar would communicate with Fo-Lan and not him, E-Poh is willing but sends four Tcho-Tchos to accompany them. They ride out onto the plateau, and Fo-Lan and Marsh promptly kill the four Tcho-Tchos. Giant, flaming humanoid figures bearing tube-like weapons descend from the sky and destroy the city of Alaozar. Satisfied, Fo-Lan and Marsh return to civilization.