The story centers around a young girl named Capable who lives in the three-house town of Frip, overlooking the sea. For longer than anyone can remember, our protagonist, her widowed father and her neighbors (the Ronsons and the Romos) have been besieged by gappers -- strange creatures that look sort of like bright orange baseball-sized burrs with multiple eyes (most hilariously depicted in Smith's illistrations). The gappers, for some inexplicable reason, manifest their love for the goats, whose milk is the town's entire economy, by attaching themselves to the hapless animals and then shreiking with joy, which causes the goats to lose sleep and stop making milk. Before long, one of the smarter gappers realizes that Capable's house is closest to the sea in which they dwell when not bothering goats and convinces the rest of its ilk to concentrate their efforts solely there, thus turning Capable's goats into massive, wailing balls of gappers, while the neighbors' herds are left alone.
The Sisyphean task of brushing away the ceaselessly returning gappers takes up all of Capable's time. Her selfish neighbors react to her pleas for help with the peculiar logic of a trademark Saunders response: "Not that we're saying we're better than you, necessarily, its just that since gappers are bad, and since you and you alone have them, it only stands to reason that you are not, perhaps, quite as good as us. Not that we hate you! We don't. We even sort of like you."
Compare and contrast: gapper vs. Kaus.