How to use the Polybius Cipher in Chinatown Detective Agency – Crack the Code lead solution

After completing Chinatown Detective Agency’s first three cases, you’re given the choice between a few people that you can work for. If you go with Rupert Zhou, you’ll start a case known as “The King and the Philosopher,” which will require you to decrypt a coded message — similar to the one featured in the Librarian Code lead — except this time, you’ll have to use a Polybius Cipher. Here’s how to crack this code.

Everything you need to crack the code will be included in an email you’ll receive from an unknown sender with the subject line, “A Locked Door.” In this email, you’ll see four strings of letters — each composed solely of letters ranging from A to E — which are all separated by forward slashes. At the bottom of the email, you’ll see five words stacked on top of one another, each of which has five letters.

The email mentions that you must crack the code using a key and also that “keys are shaped like squares” sometimes. This is a sign that you’ll need to use a Polybius Square Cipher, which effectively means you’ll have to create a five-by-five grid with both your X and Y axes featuring letters A through E — those are the only letters featured in the various strings of letters, after all. Then, since you have five columns and five rows, you can fit the five five-letter words found at the bottom of the email inside the grid. You can do this on your own by drawing it on a piece of paper, but if you want to toss a little cash Mei Ting’s way, she can set up the cipher for you at the library.

Once the cipher is set up, it’s just a matter of matching pairs of letters to their corresponding coordinates. For example, the pair of letters “AD” would correspond to the letter “T” if we’re going off the cipher shown above. Once you’ve matched every pair of letters, the decrypted code should read: “Tomorrow Nite Seven Fifteen.” This indicates when you’ll need to go to the National Gallery to progress the case.