The galley sails through the Basalt Pillars of the West. To the consternation of the investigators, it drops into a massive cataract and continues on into space.
During the trip to the moon, Markus is struck by a rock during a space storm. Later, he goes mad at the sight of a horrible larval monster.
The galley lands in the Great Lunar Sea. When Markus sees the City of the Moon-Beasts, he again succumbs to madness.
The investigators are herded through the city. Markus rescues a white cat from torture. Malcolm and John take advantage of the confusion and escape but are soon recaptured. The runaways are whipped and manacled.
They trek across the moon plains towards a large crater. Suddenly, the moon-beasts are attacked by a large number of cats.
The investigators are freed. The white cat thanks Markus for his help. The cats take them to the city of Ulthar. There they receive treatment for their physical and mental injuries. They meet the high priest, Atal. He teaches them spells and suggests a way to thwart Haon-Dor.
Seeking a way to return to the moon, the investigators meet a black cat who introduces them to his companion, a Sarrubian named Minonim-Mer. He asks them to accompany him on his quest to find his lost companions and return to Sarrub.