GLASSHEADS, pt. 5 Cover Challenge
This challenge can be found on the cover of issue 12. Spot the characters on the left edge.
The Square
We are given the word SQUARE followed by a list of number pairs.
The word SQUARE and the pairs of digits point at a Polybius square: each pair is a (row, column) coordinate into a 5×5 grid of letters.
Because a 5×5 grid only holds 25 cells for 26 letters, one letter has to be dropped (or merged).
Working out which one is the puzzle: filling the grid with the letters we already know from tficomic.io, the coordinates only line up once K is the missing letter:
A B C D E
F G H I J
L M N O P
Q R S T U
V W X Y Z
Decoding the coordinates against that grid, we get our URL.