When a lion visits the library, no one knows what to do: there are no rules about lions in the library. But soon he's indispensable - "What a helpful lion," people say. "How did we ever get along without him?" But one day the head librarian falls and breaks her arm, and the only way the lion can get help is to roar. And that is breaking the rules. The next day the lion doesn't come to the library, nor the next day, nor the day after that...until Mr McBee finds him and tells him that sometimes there is a very good reason to break the rules - even in the library!