Karen has lost her cat, Mr. Whiskers, on Friday night. She looks all over for him, and decides to put "Lost Cat" posters on trees and light posts around town.
Soon cat rescuers begin to arrive at her home with "found" cats they leave with her. By the time she has thirty-seven cats, she understands why -- she did not describe Mr. Whiskers on her poster, and every person who finds a cat delivers it to Karen.
Thirty-seven cats are a lot of cats. There are pussycats everywhere in the house, and Karen has a descriptive name for each: Purcee, Shredder, Clawdia, Groucho... all thirty-seven are painted in rich detail, and kids will enjoy matching names in the text to the illustrated cat.
Karen takes care of them for the weekend, inventing games, feeding and loving herds of cats. When she goes to buy more cat food, she sees posters for these cats too. With Mother's help, she takes each one to its home, and finally Mr. Whiskers turns up on his own, glad to be back.