Twenty astronauts aboard an interstellar "ramship" colonized the Smoke Ring five hundred years before the story begins. Their descendants have adapted their cultures to the free-fall environment. Without gravity, even those who live in integral tree tufts are much taller than Earth-average humans, having grown up in much weaker tides. Many people are able to use their longer, prehensile toes as another set of fingers. The small number of devices left from the original crew are coveted items in Smoke Ring societies.
Quinn Tribe inhabits the "in tuft" of Dalton-Quinn tree. They normally subsist on the tree's cottony foliage, augmented by hunting and a flock of domesticated turkeys. But since the tree passed near Gold six earth years ago it has been falling toward Voy, nearly dropping out of the Smoke Ring. As a result, the tribe suffers a severe drought. The tribe's leader, the Chairman, decides to send a party of nine up the tree, ostensibly to hunt and re-cut tribal markings into the trunk. The group consists mostly of cripples or people the Chairman dislikes, including the Chairman's son-in-law (and rival) Clave, and Jeffer, the Scientist's apprentice.
When they approach the midpoint they notice that the tribal markings are different; upon reaching it, they are attacked by members of the Dalton-Quinn tribe who live at the other end of the tree. During the battle a massive tremor splits the tree in half, causing the in tuft to fall farther toward Voy (killing its inhabitants) and allowing the out tuft to find a new equilibrium that is closer to the Smoke Ring's median. The seven surviving members of the Quinn Tribe and one of the attackers jump clear of the shattered tree and are left adrift in the sky with only a few "jet pods" (high pressure seed cases that provide a temporary thrust when opened) as their only method of propulsion.
Before dying of thirst, they hook a passing "moby" (a flying whale-like creature) which takes them to a "jungle," which is a floating mass of plant life. They cut loose, crash, and find themselves in the middle of a battle between the Carther States, who live in the jungle, and slave-runners from London Tree. The group is split when six of them are captured by the slavers; the other two remain in the jungle.
Carther States counter-attacks some weeks later, and the Quinn Tribe group is reunited. During the battle they steal London Tree's CARM (Cargo And Repair Module), a small spacecraft—a relic of the original settlers. The CARM is still functional due to careful management and its robust design; its solar panels provide electricity to electrolyze water into hydrogen and oxygen, which it stores automatically and then burns for propulsion as needed. London Tree's bow- and spear-armed warriors use the CARM to conduct long-distance military actions and slave raids on a scale impossible for wingless humans in a zero-g environment.
Not fully understanding how to pilot the CARM, the Quinn and Carther warriors engage its main rocket motor, which accelerates the ship at several g , enough to prevent the crew from reaching the controls to turn the motor off. The CARM is propelled up into the thinnest part of the gas torus before running dangerously low on fuel. As a result, they become the first Smoke Ring inhabitants in centuries to see the naked stars.
Unknown to any of the inhabitants of the Smoke Ring, Discipline, the ship in which their ancestors arrived, remains in orbit, and its AI autopilot, Kendy, has been attempting to watch their progress. When Kendy sees the CARM dangerously far from the habitable area of the Ring he contacts them. With help from the on-board computer and after some interaction with Kendy, the occupants of the CARM eventually safely return to the Smoke Ring. Unable to reach any of the trees that they know, they decide to settle on a new tree, which they dub Citizens' Tree.