The Oban Compendium

Origin
The Oban Compendium is a book that was written by Sumerian mystics, who we re under the influence of the Old Ones, prior to the Old Ones attempt to invade Earth. Apparently, this book was a blue print for the human servants of the Old Ones, once their invasion of Earth had been completed. The plans called for the Compendium to help the servants, and the rest of humanity, acclimate to whatever world the Old Ones would have built, had their invasion of Earth been successful. Among the information contained in the Oban Compendium was the location of the Mi-go outposts around the world.

However, the before the invasion could take place, the forces of Good and Evil went to war against the Old Ones. The Old Ones were sealed up in an empty dimension.

Like the Necronomicon, copies of the Oban Compendium were destroyed throughout the subsequent centuries, until only one was known to exist.

Napoleon acquires the Oban Compendium
This copy ended up falling into the hands of French Emperor, Napoleon Bonaparte, in 1806. Napoleon was able to decipher it and leaned of the Mi-go's Antarctic outpost. Napoleon hatched a long range plan, should he ever be defeated. He planned that most of his loyal followers would travel and settle in that outpost.

In 1812, following Napoleon's defeat, he sent those followers on that journey, who were led by Marcell Duval, one of Napoleon's most loyal friends. To keep the Oban Compendium from falling into his enemies hands, Napoleon gave the book to Duvall to take with him.

Rex Buckland uses the Compendium to save the outpost
In late 2014, Rex Buckland, Hannah Webster, and Randolph Carter, discovered the outpost and the descendants of Napoleon's followers, led by Gilles Duvall, a descendant of Marcell Duvall. While there, Rex discovered that the equipment the Mi-go had used to make the outpost, was malfunctioning and, if not repaired, could result the in the destruction of the outpost. Rex convinced Duvall to lend him the copy of the Oban Compendium, which allowed Rex to make the necessary repairs. However, Rex ended up telling Duvall that the only real chance of survival for him and his people were to re-establish contact with the outside world. Duvall agreed. As a token of gratitude, he gave Rex the copy of the Oban Compendium.

Thus the Oban Compendium is but the latest of rare books and scrolls to be added to Rex's collection.