but there is one single pit, so it cannot be anywhere else than at (1,1)

Hi @quedo - no the error is with your code. I pasted it into the editor and there's even a helpful error message explaining what is going wrong:

Returned solution incorrect for fixed string = abcdefghijklmnopqrstuvwxyz: 

'nopqrstuvwxy`abcdefghijklm' should equal 'nopqrstuvwxyzabcdefghijklm'

Your code is not mapping the letter m to z correctly. The reason is that, for m the value of c that you are using corresponds to c=122. Now insert c=122 into your code and see what value appears after your calculations.

Please read this: https://docs.codewars.com/training/troubleshooting#post-discourse