Penny Warner 
Hunt for the Missing Spy [PDF ebook] 

Cody, Quinn, Luke, and M.E. are the Code Busters-clever clue hunters with a passion for puzzles. They can’t wait for their school trip to Washington, D.C., where they’ll get to visit the International Spy Museum. But it seems as if someone is spying on them-or at least leaving coded messages that even the Code Busters can’t crack. And once they arrive at the museum, they notice they’re being followed by a mysterious stranger. Then a classmate goes missing. Could the unknown spy be responsible? It’s up to the Code Busters to find out! Can you crack the code? Test your brain with the Code Busters to see if you have the right stuff to be an ace detective. Answers are in the back, if you ever get stuck.