Answer: Secret Code #182

The secret message says:

SMILE

The shift was 13.

The secret note decoded: SMILE
The note, decoded.

Letter by letter

Secret letterFRVYZ
Real letterSEILM

Decode it with Python

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

secret = "FZVYR"
shift = 13
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:

SMILE

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.