Since Hacker has a secret device that can listen in on their conversations, Matt, Inez, Jackie, and Digit need to create a way to communicate with each other without Hacker knowing what they are saying. They decide to create a code and an accompanying ruleset so that both the sender and receiver can understand the message. Inez suggests using the page number, line number, and word number within the line of Digit's book, The Cyberchef, to communicate.
Dine (Navajo) code talkers transmit the coordinates of the enemy to the naval fleet for an attack. Because the enemy has no knowledge of their language, their communication is secret and cannot be decoded.
Beakman explains the history of code. Cryptography is the foundation of codes. Beakman then makes a DIY skytale to create a secret code. The enigma machine helped with WW2 codes and then Beakman shows how to create a DIY Grille to decode messages.