Each of the six extracts is encrypted with a simple substitution cipher
In the first extract, this is a straightforward shift: P=A, Q=B, R=C etc.
In extracts two to six, the ciphertext alphabet is formed by taking a keyword, removing those letters that occur more than once in the keyword, and then adding all remaining letters in alphabetical order.
In extract two, the keyword is MURDERS IN THE RUE MORGUE. By taking out those letters that are repeated in the keyword, we are left with: MURDESINTHOG. We then add all unused letters in alphabetical order to give us: MURDESINTHOGABCFJKLPQVWXYZ.
Finally, the alphabet is shifted to give the keyword PUZZLE as the encryption of A in each alphabet in turn (as read down the left hand side of the grid).
Solution Grid
