Ruby Redfort: Take Your Last Breath - Lauren Child

What would you do if you were a thirteen-year-old girl and a secret agency asked you to become their ace code-cracker...?
 
Super-cool Ruby Redfort has already aced one mission - sort of - but now she's all at sea. Sharks? Pirates? A giant sea monster? No problem, Buster. But diving without oxygen? Yikes! Ruby better learn fast, or she'll be feeding the fishes...