Mr. Bedford, a failed businessman, retreats to a rented bungalow in the remote village of Lympne, Kent, to write a play. Each evening, a peculiar little man in a cricket cap and cycling knickerbockers walks past his window, buzzing and gesticulating to himself, disrupting Bedford's concentration. After 14 evenings, Bedford confronts the stranger, who turns out to be Mr. Cavor, an eccentric scientist living nearby. Cavor visits three days later and offers to buy the bungalow because Bedford's presence has ruined his habitual walking route. Instead, Bedford proposes that Cavor come each afternoon to discuss his research, using Bedford as a sounding board.
Over several visits, Cavor explains he is attempting to create a substance opaque to all forms of radiant energy, including gravity. Such a substance would block gravitational attraction just as glass blocks heat. Bedford barely follows the technical details but immediately grasps the commercial implications: The substance could lift any weight effortlessly, transforming industry and transportation. He envisions a vast monopoly and insists on becoming Cavor's business partner.
On October 14, 1899, a dispute among Cavor's laboratory assistants causes the furnace fuel to run out. The experimental alloy cools prematurely, completing the manufacture of Cavorite while Cavor is away. Because the Cavorite has formed in a thin sheet, the air above it suddenly loses all weight, and the surrounding atmosphere rushes inward and upward with tremendous force, creating a violent vortex that destroys Cavor's house and permanently deafens Bedford in one ear. Cavor explains that had the sheet not been blown loose, it would have created a permanent atmospheric fountain capable of stripping Earth of its air. They blame the destruction on a cyclone and rebuild the laboratory.
Cavor proposes building a spherical vessel coated with Cavorite, large enough for two passengers, constructed of steel lined with glass. The Cavorite shell is divided into sections that function like roller blinds: When all blinds are closed, the sphere is shielded from gravity and flies in a straight line through space; when a blind is opened, the sphere is pulled toward whatever massive body lies in that direction. Bedford's skepticism gives way to visions of interplanetary commerce, and the two work feverishly through the winter to build the sphere.
On a still evening, they climb inside with compressed food, oxygen cylinders, and reading material. The blinds close, and they hurtle into space, experiencing weightlessness and viewing the stars with breathtaking clarity. The journey passes in a dreamlike state. As they approach the moon, Cavor frantically manipulates the blinds to control their descent. They crash-land in a huge crater, bouncing through frozen air before coming to rest in shadow. Lunar sunrise brings violent transformation: The frozen atmosphere thaws rapidly, creating torrents that tumble the sphere and knock Bedford unconscious. When he wakes, seeds on the exposed soil are growing at an astonishing rate, transforming the barren crater into a dense jungle of alien vegetation.
They test the atmosphere, find it breathable, and emerge. The moon's gravity, one-sixth of Earth's, sends their first steps into enormous, uncontrolled leaps. Giddy with elation, they bound farther and farther from the sphere until they realize it has disappeared beneath the rapidly growing plants. As they search, deep booming and metallic clanging rise from underground. They glimpse the moon's inhabitants: enormous, nearly brainless creatures called mooncalves, 80 feet in girth, herded by Selenites. The Selenites are compact, insect-like beings barely five feet tall, wearing leathery garments, spiked helmets, and goggles. The two men also discover a circular metal lid that opens to reveal a shaft descending into the moon's interior. Desperate with hunger, Bedford eats a fleshy red fungus that proves intoxicating. Both men become recklessly drunk, stumble upon a group of Selenites, and are seized and dragged underground.
They awaken chained in darkness deep within the moon. A Selenite enters without its helmet, revealing its true face: no nose, bulging side-set eyes, a downward-curved mouth, and a triply jointed neck. The Selenites feed them mooncalf flesh. Cavor proposes using geometric demonstrations to communicate, but the guards prod them forward with goads through immense caverns. At the edge of a vast abyss spanned by a narrow plank bridge, Bedford refuses to cross. When a guard stabs him, he snaps, breaking his chains and striking the Selenite, whose body shatters with shocking fragility. He kills a second guard and frees Cavor; the remaining Selenites scatter as the two men flee through the tunnels in enormous leaps.
Hiding in a side cavern, they argue bitterly: Cavor blames Bedford's violence for ruining any chance of peaceful communication, while Bedford insists it was necessary for survival. Hearing pursuit, they climb upward and emerge into a vast cavern where Selenites are butchering mooncalf carcasses. Attacked with spears, Bedford seizes a heavy gold crowbar and charges. Despite being shot through the shoulder, he fights through the fragile Selenites, and the two race toward faint daylight, emerging onto the crater surface in the late lunar afternoon.
With days remaining before nightfall brings lethal cold, they separate to search for the sphere. Cavor expresses deep misgivings about bringing the secret of Cavorite back to Earth, fearing it will enable warfare. Bedford finds the sphere but, returning to signal Cavor, discovers only Cavor's cricket cap amid trampled vegetation and a blood-smeared note. Cavor writes that he is injured, hunted by Selenites with larger brain cases, and intends to surrender. The note ends abruptly in a pencil streak and blood. The first snowflake falls, and Bedford is alone.
With the atmosphere freezing, Bedford leaps back to the sphere, seals it, and activates the blinds as darkness engulfs the moon. Through more luck than skill, he navigates home, spending weeks in silent space experiencing a profound dissociation from his identity. He splashes down near Littlestone, Kent. Friendly bathers help him ashore with two gold crowbars, but while Bedford is at a hotel, a boy discovers the sphere on the beach, accidentally triggers the shutters, and is launched irretrievably into space. Bedford is stranded with no sphere and no proof. He deposits his gold under an assumed name to avoid his creditors and relocates to Amalfi, Italy, to write his account.
Months later, Bedford learns that Julius Wendigee, a Dutch electrician, has been receiving fragmentary radio transmissions from Cavor on the moon. Cavor is alive and living freely among the Selenites. His messages describe the moon's interior as a vast sponge of rock honeycombed with caverns, with shafts descending to a subterranean Central Sea of glowing water. He details the Selenites' social organization, in which each individual is physically shaped from birth through training and surgery to fit a single function. Intellectuals with enormous brain cases form a ruling class, while idle workers are drugged and stored in fungus fields. Cavor is brought before the Grand Lunar, the supreme ruler, whose brain case measures many yards across. The Grand Lunar questions him about Earth and reacts with horror when Cavor describes human warfare. The Grand Lunar presses Cavor for the method of making Cavorite, which the Selenites understand theoretically but cannot produce because the moon lacks helium. The transmissions grow increasingly disrupted by apparent Selenite interference. After days of silence, one final transmission arrives: Cavor admits he was foolish to reveal his knowledge, then begins dictating the Cavorite formula before the signal cuts off permanently. No further messages are ever received, and Bedford is left to imagine Cavor being dragged from his apparatus into the silence and darkness of the moon.