Answer: Secret Code #136

The secret message says:

SKATES

The shift was 5.

The secret note decoded: SKATES
The note, decoded.

Letter by letter

Secret letterFJPXY
Real letterAEKST

Decode it with Python

This program does the decoding for you. Change the secret and the shift to crack other messages!

secret = "XPFYJX"
shift = 5
message = ""

for letter in secret:
    if letter.isalpha():
        number = (ord(letter) - ord("A") - shift) % 26
        message = message + chr(number + ord("A"))
    else:
        message = message + letter

print(message)

When you run it, it prints:

SKATES

Did you know? Shift codes are very old. A Roman writer called Suetonius said that Julius Caesar wrote secret letters by shifting the alphabet by three. That’s why it’s often called the Caesar cipher.