Knowing now that his mother was murdered by the evil Mauricio Valls, Daniel Sempere has been trying to locate him, consumed by desires of revenge. The story is now moved, however, by yet another old memory of Fermín's ever-changing past: a child he once tried to save, now turned into the beautiful and ruthless Alicia Gris, a member of a secret operative for the Francoist police, who will team along with veteran Captain Juan Manuel Vargas to try to find the disappeared Valls. Alicia soon discovers a much darker story, related to the mysterious banker Ignacio Sanchís and a variety of sinister characters, where crimes and betrayals form a tree whose roots sink deep down in the Spanish Civil War.
Starting from where The Prisoner of Heaven stopped, the book puts an end to the tetralogy of The Cemetary of Forgotten Books. Some short stories, either directly or indirectly set on the same universe, were published in a compillation named The City of Vapor, released after Zafón's death in 2020.
This work contains examples of:
- Ambiguously Bi: Alicia has some Ship Tease with Vargas, yet also imagines herself forcefully kissing Bea.
- Ambiguously Evil: Alicia feels betrayed when she discovers Leandro lied about Rovira, as the latter turned out to work for the former and not for the police as claimed. However, while evil and an accomplice of Francoist state crimes, Leandro seems to be sincere when he touts Alicia as his surrogate daughter and claims Rovira was only supposed to observe Alicia before going crazy on her. His death itself is a very explicit Suicide by Cop, forcing Alicia to kill him even when she was unsure about what to do, which only leaves Leandro's true nature unrevealed.
- Artistic License History: In-universe for comedic effect. Fermín claims the inventor of the submarine was a guy named Isaac Monturiol, which effectively conflates two real life developers of functional submarines, Isaac Peral and Narciso Monturiol.
- Big Bad Duumvirate: Leandro Montalvo and Gil de Partera, with the possibly addition of Minister José María Altea as their boss.
- BrotherSister Incest: Zig-zagged. Ignacio Sanchís and Victoria Ubach seem to be half-siblings when it is implied Sanchís is Miguel Ángel Ubach's bastard son, but it then turns out that Victoria is actually Ariadna Mataix.
- Continuity Drift: Fermín's past is revisited and rewritten for a second time in the tetralogy, now including a subplot about the daughter of a friend he tried and failed to save.
- Cryptic Background Reference: Ladislao Bayona and Enrique Marqués are mentioned as authors from David Martín's generation, but nothing is known about them.
- Evil Versus Evil: Sanchís is attempting to get revenge on the corrupt Valls, who participated in a grat-scale baby thief operation, but Sanchís himself is a Morally Bankrupt Banker who cons elderly people out of their homes.
- Femme Fatale: Alicia is a sultry female detective who often wears in black.
- Good Counterpart: Valentín Morgado seems to be this to Vicent Carmona, as they serve Sanchís and Valls respectively, but it turns out Sanchís is not fully clean either.
- Ill Girl: Two in the story: Elena Sarmiento, Valls' wife, as well as Susana, Víctor Mataix's.
- MayDecember Romance: There's some degree of subtext between Alicia and Vargas, even although the latter is old enough that his dead daughter was born the same year as Alicia. Some Like Parent, Like Spouse might be on play for Alicia's part, as Vargas has coincidentally the same first name as her father (although not the second).
- Meaningful Name: Rodrigo Hendaya, the stylish Francoist inspector. His first name evokes El Cid, a historical figure Francoists loved to glorify (and subject to heavy revisionism in the process), while his surname references the Meeting at Hendaye between Francisco Franco and Adolf Hitler.
- Morally Bankrupt Banker: Miguel Ángel Ubach and Enrique Sarmiento were the first in the story's timeline. Ubach's place is occupied by Ignacio Sanchís by marrying his daughter Victoria.
- No Celebrities Were Harmed: Sergio Vilajuana is obviously based on Sergio Vila-Sanjuán, a real life journalist and writer whom Zafón was a friend of.
- No Name Given: Subverted. Daniel's father had gone unnamed for all the three previous books, but here he's revealed to be named Juan.
- Only One Name: Juan Manuel Vargas' first name is said exactly once in over 900 pages. The rest of the time, he's either Vargas or Captain Vargas.
- Posthumous Character:
- Ricardo Lomana, Alicia's former mentor and sexual harasser, was killed before the story started.
- The shadow of Francisco Javier Fumero still glides over the story, as both Lomana and Hendaya are revealed to be his former apprentices.
- Remember the New Guy?:
- Víctor Mataix is said to be among David Martín's close friends (as well as another character, Alfons Brósel) and one of the other great niche writers of his time, despite being mentioned for the very first time in this novel. This also ignores that Martín was a bitter, friendless man, although by this point this portrayal is non-canon due to the entire Angel's Game having been retconned as delusional memories.
- Another entirely new character, Sergio Vilajuana turns out to have been a close friend of the Sempere family who also knew Mataix and Martín.
- Juan Antonio Gris, Alicia's father, turns out to have been another close friend of Mr. Sempere and inhabitant of his neighborhood that had been never mentioned.
- In this book, failing at saving Alicia was a gigantic Heroic BSoD that accompanied Fermín for a long time. However, absolutely nothing about her had been mentioned in both versions of his past from the first two books of the tetralogy, even although his flashback from the third installment happened immediately after losing Alicia.
- The Vamp: It's astonishing the number of men who are immediately attracted by Alicia, which she capitalizes on in her job.