Description Mac B. is on another secret mission in this totally true kid spy adventure from New York Times bestselling author, Mac Barnett! The Queen of England calls on her trusty spy, Mac B., once again. This time, Mac must navigate secret tunnels beneath the Berlin Wall in order retrieve cheat codes from a Soviet scientist. Floppy disk in hand, our hero finds himself trapped in East Germany, stuck between the wall and the Stasi. How will he escape? Well it is 1989, and walls do fall down.