Skybound takes place on the Thundering Isles. The Thundering Isles is a group of floating islands cast up into the sky for unknown reasons long before the current memory of the Clans.
The Thundering Isles is suffering from hundreds of years spent isolated from the ground, and with many, many cats living on it. Prey is running shorter every year, and the three Clans are left desperately battling for resources and a way to keep on living.
Medicine cats are receiving grave, if vague, warnings from StarClan. Something must be done to steer the fate of all these cats away from disaster, by any means necessary.