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In 1930s Ashiya, the timid shopkeeper Shozo is pushed by his scheming mother into divorcing Shinako and marrying the younger Fukuko, who brings a dowry. Shinako writes to Fukuko asking for Shozo's aging tortoiseshell cat Lily, calculating that the cat will draw Shozo back. Fukuko, jealous of Shozo's devotion to Lily, agrees and makes him hand the cat over, and the cat's new home becomes the pivot of all three characters' schemes.
In this novella, the handling of Lily carries meanings about the marriage that the characters do not state outright. Fukuko's giving the cat away, Shinako's taking it in, and Shozo's secret visit to see it each say something about who holds his affection, and the comedy comes from reading those messages beneath the surface of ordinary acts.
Shinako takes Lily as a tool to win back her husband and at first resents the cat. Daily feeding, sharing a cramped room, and seeing her own rejection in the discarded animal turn the tool into a companion. Caring for something for strategic reasons can rewrite the caretaker's motives, and the original purpose loses its hold.
Shozo appears too weak to decide anything, and his mother, his ex-wife, and his new wife negotiate his life around him. The narrator suggests, though, that he used this look of helplessness to get rid of Shinako while leaving the responsibility with others. His passivity is partly real and partly a cover for choices he would rather not own.