The Treasure of Melifex the Mad

From publisher blurb: Adventure Module MX-02 An adventure for level 3 characters Your party has braved the tricks, traps, and horrors in the laboratory of Melifex the Mad and returned with his prized magical research. Unfortunately, the crafty wizard has coded all his works with a cipher, making them worthless until the cipher is found. Finding the cipher poses your greatest challenge as possessing it could be the key to unlimited magical power and riches. Then again, it may just earn you a dagger to the ribs. You may have to find the cipher just to stay alive.