Beginning

Even before the events described in the book, Doono with Fuksiya and Selyodochka from Sun City visited the Moon and brought out the moon mineral with extraordinary properties (later called lunit). After a number of events it turns out that its rapprochement with the magnet gives the effect of local weightlessness that can allow to send to the Moon a spaceship with large crew and supplies on board. As Doono hopes, there is intelligent life over there, which due to the loss of the atmosphere has moved inside of the Moon. The cosmonauts take the seeds of terrestrial cultivated plants with them. However, the exclusion of Dunno from the flight for stealing the weightlessness device from the Pavilion and careless handling of it, which nearly led to its loss, brings to these plans unexpected adjustments. Dunno instigates Roly-Poly, who was also not included into the crew, to fly as stowaways. The day before the launch they snuck into the rocket. At night before the flight Roly-Poly has changed his mind, but instead of getting out of the rocket accidentally launched it into flight in automatic mode.

After the Moon landing Dunno and Roly-Poly come out in space suits for a walk to a nearby mountain. In a cave Dunno falls into an icy tunnel leading down to the internal cavity of the Moon and slides down, apparently sitting down, thereon in the sublunary space. Going down on a parafoil, he finds on the inner core of the Moon (which the locals call the Earth, too) with the civilization of the same shorties, but living according to the laws of capitalism. The size of lunar plants, in contrast to terrestrial, is proportional to the height of the shorties so they appear to be undersized for Dunno. Roly-Poly, after losing Dunno, runs in panic back to the rocket.

Being on the Moon, Dunno, unfamiliar with the concepts of money (lunar currency — "ferting" (author-derived from British "farthing") consisting of a hundred of "santik" (author-derived from French "centime")) and private property is always getting into unpleasant situations. At first, he appears in the garden of Mr. Klops and eats his raspberries, that's why he was grabbed and hounded by order of Klops as a thief. Dunno, fortunately, managed to escape over the fence, while he did not understand what was, in fact, his fault. Then he was taken to jail for refusing to pay in a street cafe, where during registration through a system of identification using simplified Bertillon method he was mistakenly identified as the famous gangster Pretty Boy (Красавчик), as a result the police were extorting a bribe, and Dunno's refusal and complete misunderstanding of the situation were regarded as intractability and he was placed into a prison cell. There he met unemployed shorty Kozlik and small crook Miga. Miga believed the story of Dunno about the seeds of giant plants, helped him to avoid a scuffle in the cell, and before the release of Dunno from prison gave him a letter to his friend, arms dealer Zhulio.

After leaving the jail Dunno and Kozlik come to Zhulio. He makes a bail for Miga and all four are discussing the prospects for growing terrestrial plants on the Moon, the seeds of which were left in the rocket on the Moon surface. To raise funds for the construction of an aircraft capable to reach the outer Moon surface, they start a joint-stock company called "The Society of Giant Plants", whose shares are secured by future shares of prospective seeds (i.e., at the beginning of the company's activities it is actually a consumer cooperative). In doing so they promote the fact of Dunno's arrival as an cosmonaut in mass media and using methods of outdoor advertising (it was especially effective in the countryside, whose residents, as a rule, do not buy newspapers). Gradually the shares are selling. Their activities are disturbing the local monopolists, because appearance of giant plants threatens them with devastation. Spruts, their leader, the largest landowner and owner of the textile and sugar factories, takes measures to collapse their company. He bribes Miga and Zhulio, and they run with the cash received for the shares, leaving Dunno and Kozlik to their fate. At the same time fragmentary allusions to the fraudulent nature of the company, launched by the editor of Spruts-owned newspaper, Grizzle, lead to a panic among small shareholders. Remaining unaware about what was happening Dunno and Kozlik are forced to flee, and go to San Komarik. Not finding there Miga and Zhulio, they have found themselves on the dark side of life. They wander, with hunger and disasters in flophouses without any work.

Meanwhile, stock traders Zhmurik, Teftel and Hanakonda are buying huge batch of the Society's shares on an upward trend, and are taking steps to rectify the situation of their cheapness by entering an information war in the media against Spruts' newspapers. Skuperfild, the owner of the pasta factory, being in the dark about the backstage war of financial speculators, spent almost all capital buying Society's shares, but Spruts deals a decisive blow: he published the documentary details about the collapse of the company. All shares have depreciated at one moment, and as a result Skuperfild was on the verge of bankruptcy. In desperation, he reduced his workers' pay down to half — initially workers threaten to strike, and then have declare it. Then Skuperfild decides to recruit new workers among the inhabitants of flophouses in San Komarik. Among those hired were Dunno and Kozlik. Cars with new employees have arrived in Brehenville. According to the Skuperfild's plan, they should immediately get to work. But striking regular workers becomes aware of this trick. The strikers organize a defense - in cold blood they push newcomers away from Skuperfild's factory and begin to frantically chase them all over the city, as a result unfortunate Dunno and Kozlik are thrown into the river. Dunno lost shoes, Kozlik lost hat. To earn some money, Kozlik takes Dunno's hat and goes to the city, Dunno remains under a bridge. There he soon met a group of other homeless. Kozlik failed to scrape up a santik in a strange city, he came back with nothing. They dined a piece of bread, that one of the tramps (Bubble) gave them and stay with tramps overnight. Police shut down lights on the embankment and arrested whole company in the middle of the night, except Bubble, who was able to take out one of the attackers with his own stun baton and escaped down the river on an inflatable rubber pillow. In the end Dunno and Kozlik sent to The Fools' Island for the sleeping outside and for not having boots and hat. On Fools' Island lunar shorties in course of time turn into rams exposed to harmful air.

Roly-Poly, after abandoning Dunno to his fate, is trying to stifle the voice of conscience with continuous absorption of food. Eventually, he ate a year's supply of food in the rocket in four days. Deciding to go in search of food, he returns to the cave, falls inside of the Moon, but as a result of rotation of the "inner Moon" found himself in another place. Unlike Dunno, Roly-Poly, as a more cautious and practical shorty, quickly learns the essence of commodity-money relations. In addition, he gets lucky from the outset and he opens a new market niche — sale of salt. He quickly gets richer, hires workers for the salt production, but soon go bankrupt, unable to compete with owners of large factories, led by Dracula — the owner of the coast with raw salt. After the bankruptcy Roly-Poly becomes "Twister" — a worker at an amusement park, actuating rides. After some time he joins the "Society of Free Twisters" (Trade union analogue).

Expedition from Earth

Doono with friends found disappearance of the rocket with Dunno and Roly-Poly on board, and organize a rescue mission. Having built a new multistage rocket FaH ("Fuchsia and Herring"), 12 shorties led by Doono go to the Moon. Having found big rocket (called "DaR" ( "Dunno and Roly-Poly")) empty, they go in search of Dunno and Roly-Poly and discover the icy corridor leading to the inner cavity of the Moon. Having discovered large deposits of lunit and antilunit (Mineral which levels effect of the lunit, with a smaller radius of action than lunit), Doono and his companions go down in a rocket on the ice corridor.

However, lunar astronomers employed by Spruts inform him about the arrival of the new rocket. Therefore, while approaching city of Fantomas rocket was fired upon and Doono has been forced down in the countryside. Police raid on earthlings ends in complete failure after the use of weightlessness by Doono.

Earthlings have founded the "Space City", come into contact with the villagers, give them the seeds of giant plants, as well as supplying all of them weightlessness devices and antilunit. Armed with this "terrible power" — weightlessness, they overthrow the capitalists. Roly-Poly came out to another "Twisters" during all of these events and tell them that he's alien. They sent him on train to Fantomas, from where he reached the "Space City". Roly-Poly offered to search for Dunno on Fool's island. Earthlings arrived in Los Paganos and seized one of the ships. With the help of the captain Rumbik, familiar to Roly-Poly, characters get to the Fool's island and rescued Dunno and Kozlik, who already begun to turn into a ram, and other doomed shorties. Dunno offers to bury weightlessness device in the middle of Fool's island so harmful air, converting shorties to rams, went up and the fresh sea air would start come to the island. But it didn't come to that. (You never know where it will go with the wind). Characters come back with Dunno and Kozlik to the "Space City". Dunno feels bad. Dr. Pillman diagnosed him with an acute nostalgia and noted the need for urgent return to Earth. Despite the sabotage of Spruts and Zhulio, who blew up the FaH rocket, earthlings fly away using propellers at spacesuits and the device of weightlessness. On the surface of the Moon, they boarded the DaR rocket and made their way back to Earth. Once home, Dunno immediately healed, and declared that "now we can go somewhere on a journey again."