In this 9th book in the series, Amy and Dan travel to Jamaica and learn who the Man in Black is. I won't say who he is, you'll have to read it yourself. They also find out more about Nellie Gomez, their au pair. They also learn more about the Madrigal branch of the Cahills.
Similar titles: All of the other 39 Clues books in the series.
Yes. It's an awesome book series and online game!