It's been months since Evie and Andrew's mother mysteriously disappeared, leaving only a cryptic note. Then one day they received a mysterious package. Could it be from their mother? What should they do? And what does their unusual neighbor know? They also meet someone from their mother's past who helps them learn to create and break codes. And they find out three important facts: 1: Their mother is a spy. 2. She was forced to go into hiding. 3. They're the only ones who can save her.