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The Book of Deiwos is a large, white leather-bound book in the House at the End of the World. It is the counterpart to the Book of Daeva and the Book of Dweia. It was presumably created by Deiwos

The Book of Deiwos is capable of magic or 'miracles'. Althalus and Dweia are able to use the book by saying different words to perform said magic or miracles.

The Book first appears when Ghend hired Althalus to locate it at the House at the End of the World. Althalus learns to read and understand the book for the next 2500 years, learning also how to use it. 

At the end of the story, the Book of Deiwos and the Book of Dweia combine efforts to burn the Book of Daeva.