Prisoner of Heaven, by Carlos Ruiz Zafon (Translated from Spanish by Lucia Graves)
This is the third in a cycle of novels that began with The Shadow of the Wind and The Angels Game. I would recommend that you read the first two books before reading this one.
This novel is set like the others in Barcelona, Spain. The main character is Daniel Sempere, who, together with his father runs Sempere and Sons Bookshop. There is also another fascinating place, “The Cemetery of Lost Books” a huge library of old forgotten books protected by an elite of old bookkeepers. According to tradition initiates are allowed to select one book from the collection and must protect it for life.
The saga starts with The Shadow of the Wind and then is continued in The Angels Game which is actually a prequel. There are a lot of doings and plots and run ins with the Fascist authorities under General Francisco Franco.
Prisoner of Heaven recounts the imprisonment of Fermin Romero de Torres in a notorious political prison run by the Franco regime during the Spanish Civil War. Fermin is a character in the first two books, but not the main character. He is something of a rogue, a bon-vivant, and protector of Daniel. He escapes from the wretched prison using a technique gleaned from The Count of Monte Cristo.
There is romance, intrigue and shadowy forces in these books. I highly recommend them.