Books like The Code

Leaving only a cryptic note, Andrew and Evie's mother vanishes on their eleventh birthday. Now, almost a year later, the twins receive a mysterious package from someone named Spy X. They soon learn that the contents of the box will lead them on an incredible journey toward finding their mother - and into a world where no one's identity can be trusted. In Book #1, Andrew and Evie aren't initially sure what to make of the package that arrives at their door soon after they move to a new town.