Answer: Secret Code #153

The secret message says:

OWL

The shift was 19.

The secret note decoded: OWL
The note, decoded.

Letter by letter

Secret letterEHP
Real letterLOW

Decode it with Python

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

secret = "HPE"
shift = 19
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:

OWL

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.