The family lived in a crowded house. Ten people in one room can lead to a lot of arguments. The wife is telling the wise, well-traveled fishmonger about this problem while at the market one day, and happens to finish up her tale of woe with the words "It couldn't be worse."
The fishmonger decides to show her that it could, although he doesn't pitch the idea to her in quite that way. One by one over the next several days he advises her to bring the family's animals into the house with them, adding another each time she returns to tell him how things are going. Sure enough, it gets worse, which is probably not what the wife thought the wise fishmonger's advice would do for her. It is certain that she doesn't catch on, because each time she complains to him about things at home, she uses the same line, and he counters by telling her to add another occupant to the house.
Finally, when all of them are in the house, he gets her to take them all out - and it feels so much better! To her mind this proves, after all, that the fishmonger is such a wise man.
While this book is described in the press release which accompanies it as a classic Jewish folk tale, I happen to know that the basic story survives in a number of cultural traditions, including the Alaskan Yupik people and the Slavic people of eastern Europe. In most of the versions I have seen it is the husband who goes off to ask for advice, which he usually gets from some sort of a wise woman. The outcome is the same in each case.
Van Kampen's version of the tale reverses the major roles and changes a few of the details, which just goes to show how various oral traditions work with their own themes. Her book is well told and delightfully illustrated.