"Mum’s cross with me,” said Jennifer. "It’s Mrs. Green’s fault,” said Henry. But just who is Mrs. Green? Henry knows that Mum is cross because Mr. Moon had bumped her car; and Mr. Moon had been careless because he was fuming at being called "stupid” by his wife; and she had been so irritable because she had been hurried in the supermarket. And so it goes, like a line of cascading dominoes. There is a whole chain of very recognizable, silly scenarios to absorb before the identity of Mrs. Green can be revealed--her high heels tapping about in the apartment above had started the whole chain of bad temper!