Then write down the key from the Scroll of Waves, with the enciphered message directly underneath it, e.g.

p atte ...
y iupj ...

Now, P is 16 and Y is 25 in the numbered alphabet. 25 minus 16 is 9, and the 9th letter is I.
Similarly, A is 1 and I is 8; 9 minus 1 is 8, and the 8th letter is H,
T is 20 and U is 21; 21 minus 20 is 1, and the first letter is A
The next one is a bit different, because T is 20 and P is 16 and 16 minus 20 gives a negative number. So what you do is to add 26 (the number of letters in the alphabet) to the 16 to get 42, and then subtract the 20. This gives you 22, and the 22nd letter is V.
E is 5 and J is 10; 10 minus 5 is 5, and the 5th letter is E,
and so on

So the first two words are "I have"

If you want the maxi-spoiler, SELECT the hidden text between the highlights to obtain the deciphered message.

Highlights on
"I have found the tomb of master kelwin and have deduced the code from his notes. It is north east south west and center. My job is done and the debt paid. Good luck."