Archaeologist Dr. Nina Gould swears she is making a new start away from the toils of the past few years and decides to purchase an old house in her former hometown of Oban, Scotland. But little does she know that the house comes with an unsavory history, one that is a bit too close to comfort; especially when an old university friend looks her up and introduces her to a mysterious and odd American lecturer with a family history connected to her house.

When Sam Cleave assists the agents of MI6 to gather intelligence on a corrupt Dutch financier, he finds out that the embezzler is in fact a member of the council, the veteran society managing the Order of the Black Sun. With his investigation of the man, Jaap Roodt, Sam finds out that Nina's life is in danger. She stands in the way of the completion of the Longinus, a fierce and deadly biological weapon set to destroy the world and facilitate the Nazi ritual to bring back the Old Gods by means of the manipulation of advanced physics. Sam needs to find her before the council's assassins do.

To obtain the arcane information needed to complete the Longinus, the Black Sun sends Dave Purdue to retrieve it from a place that might or might not even exist - The Library of Forbidden Books. While looking for the deadly codes he needs to collect, Purdue is reunited with Sam and Nina, who are fleeing from the assassins of the council while accompanied by Nina's old university friend and the strange American lecturer.

But when they all team up to find the knowledge held in the legendary library, they realize that not all of them have the same intentions for the information contained therein. Which of them have nefarious agendas? And which of them are honestly trying to avert the release of the dreaded biological agent?

It is a question that can only be answered within The Library of Forbidden Books....