Lilly the mouse loves her little brother before he is born - she gives him things and sings to him. But after he is born, she is openly and very funnily hostile. Her parents think Julius is wonderful. 'Julius is the baby of the world,' they say. Lilly must share her room with him, and she wants to know if she can have it back when he goes away. 'Julius isn't going anywhere,' her parents say. Lilly tries to make him disappear by magic; she sticks pins in a toy mouse; she tells him horrid stories; and she spends a lot of time in the 'uncooperative chair'. Her parents try to be extra kind to Lilly, but nothing works. Then, at a party, when everyone is hovering over Julius admiringly, Lilly's cousin says she thinks the baby is disgusting. Lilly is instantly defensive. She makes the cousin say, 'Julius is the baby of the world'. Afterwards, she believes it herself. Lilly is realistically if over-the-top jealous, and the fact that the family is mice gives the story a bit of distance.