The book follows Lucas Corso, a book detective who is hired to authenticate a rare manuscript by Alexandre Dumas. As he delves into the investigation, he finds himself entangled in a mystery involving two other books: a rare edition of "The Three Musketeers" and a satanic text, "The Book of Nine Doors of the Kingdom of Shadows". The narrative becomes a complex puzzle as Corso uncovers connections between the books, while also dealing with a seductive woman who seems to have stepped out of a Dumas novel, a mysterious killer, and a group of bibliophiles obsessed with Dumas. The lines between fiction and reality blur as he gets closer to the truth.

"Pereira Maintains" is a novel set in the backdrop of 1938 Portugal during the fascist dictatorship of Antonio de Oliveira Salazar. The narrative follows Pereira, a widowed, overweight editor of the culture section of a second-rate Lisbon newspaper, who becomes politically awakened after meeting a young anti-fascist. As he grapples with his conscience, he risks everything to help his new friend and his pregnant girlfriend escape to safety. The story is a compelling exploration of the struggle for moral integrity in a climate of political oppression.