The two funniest characters, I thought, were the Thomson Twins because they kept on making mistakes while saying "It could happen to anybody," and still saying they were right. Their personalities were amusing.
The general story was that Lady Castafiore, a famous opera singer, was coming to stay at the Captain and Tintin's house. Lady Castafiore assumed everything was about her, whenever anybody talked about a problem she'd caused she waved it off as if they should feel honoured just to speak to her; she was not very good at seeing other's points of view. She was very protective of her jewels. The most expensive and valuable of these was the eponymous emerald. She was paranoid, constantly thinking her jewels were stolen when actually she'd just misplaced them. Eventually the emerald is actually stolen. At first everyone but Tintin believes it's the gypsies who've been living in the area who are responsible. But Tintin is determined to prove the gypsies' innocence. He investigates and finds out many things about the people in the house and eventually finds the culprit.
While I did like this book there are certainly things I would change. For example, I'd appreciate a quick back story on each character because it took me a while to understand why someone as young as Tintin had travelled all around the world having adventures and was now living with the Captain in a big posh house with his own butler. Because of this frustration I'm giving it 67 out of 100.