The second manuscript sends Corso on a quest. While the Dumas fragment is seemingly a simple matter of verifying its authenticity, the same can't be said for his other assignment. There are only three known copies of The Nine Doors in existence. A famous book of the occult written in the 1600s, its printer was burned at the stake, and all other copies of the text that could be located were committed to the flames.
Supposedly the illustrations in the book hold the key for summoning the Devil. A client of Corso's has managed to lay hands upon a copy, and asks Corso to compare it to the two known authentic copies in existence in an attempt to verify the authenticity of his own. But as Corso traipses around Europe with these two texts in his luggage, things start to happen and events spiraling out of his control.
Who is the mysterious man with the scar who keeps appearing on the periphery of his sight no matter what town he is in? Who is the strange young woman who attaches herself to Corso claiming she is there to protect him? Protect him from what and from whom he wonders?
He should wonder, because he is starting to leave a trail of bodies and damaged books behind him. He manages to get in and visit with each of the two owners of the other copies of The Nine Doors and compare the texts. But within 24 hours of him being their guest, both are dead and their copy of the text has been burnt, minus the nine engravings. Those had been removed prior to the books' destruction.
Corso had already deduced that there were minor differences in some of the engravings from book to book. What is the significance of those differences, and why has the murderer destroyed the text but retained the engravings? Is Corso at risk of the same thing happening to him? Is that why the man with the scar is following him? What, if any, connection is there between the Dumas manuscript and The Nine Doors?
These are the mysteries Corso is faced with as he races across Europe looking to such diverse sources of help as the text of the The Three Musketeers, Sherlock Holmes and his powers of deduction, and two of the finest book-forgers in Europe. All the while he is forced to stay under cover as he is now under suspicion for the murders of the two late owners of The Nine Doors.