Published in 1902 it contains translations of writings found hammered in unknown writing, onto copper sheets discovered in Guatemalan ruins. The writings are a set of prayers and libations to a God called Hastur. Included amongst them is the full text of the prayer carved onto the stones at Springer Mound and instructions for the creation and use of The Chime of Tezchaptl.

• The Codex was discovered by the players in Lawrence Bacon's house - open on his desk.
• Andrew Saunders studied the book, and was able to discover several prayers of a seemingly magical aspect from the text.
• The party took the book (and chime) with them on their trip to Carcosa, and gave it to Alexander Roby, so he could learn the magical abilities of the Chime of Tezchapt.
• It is believed that the book (and chime) disappeared when Carcosa departed earth.