Some old text adventures "encrypt" all their text with "XOR $FF" encryption.
The xor.py tool xor's every byte in the input file and write the result to inputfile ".decoded".
The result can be inspected in an editor that doesn't mind a lot of garbage bytes.
Run it on the sample:
python xor.py prisoner.bin
or
python3 xor.py prisoner.bin
or whatever.
I'm not a Python expert.