A fantasy novel for young adults, American author Ransom Riggs’s
Library of Souls (2015) is the third book in a tetralogy that includes
Miss Peregrine's Home for Peculiar Children (2011),
Hollow City (2014), and
Map of Days (2018), all of which focus on a group of "peculiar" children and young adults who possess a "second soul" that manifests transformative, supernatural properties. The protagonists of the series are two teenaged "peculiars," Jacob Magellan Portman and Emma Bloom.
At the end of the previous book,
Hollow City, Jacob and Emma, along with their talking dog companion, Addison, escape from a "time loop" into a phone booth located in the present day. Jacob has just discovered a new manifestation of his second soul: he can see the otherwise invisible "hollowgasts," antagonistic, tentacle-mouthed ghosts who feed on the souls of peculiars with the aim of restoring their human form. Moreover, Jacob can exert a limited amount of control on a hollowgast, an invaluable advantage in the fight to come. After repelling a nearby hollowgast, Jacob escapes the phone booth along with Emma and Addison. They immediately set off in an effort to rescue their peculiar friends who have been kidnapped by "wights," the name used for hollowgasts who have restored their human form.
Their search takes them to Devil's Acre, a run-down village run by wights and populated by drug-addicted peculiars. These peculiars take a drug called Ambrosia that when poured into the eyes, imbues the user with increased physical prowess. For their own profit and entertainment, the wights organize public fights between Ambrosia-enhanced peculiars and hollowgasts. Bewildered by the awful scene before them, Jacob and Emma let their guard down, allowing Addison to be captured. Fearing capture themselves, Jacob and Emma take refuge with a man who calls himself Bentham. Shortly thereafter, the two are shocked to learn that Bentham—who is also one of Miss Peregrine's brothers—is the one responsible for the botched experiment that brought the hollowgasts into being.
Fearful that they have fallen into another trap, Jacob and Emma try to run from Bentham, but he stops them, insisting he is on their side. As proof of his loyalty, Bentham tells them how they can infiltrate the wights' headquarters to save Addison. In the process, they even align themselves with a hollowgast captured in a cage that helps them inside the headquarters. This reveals to Jacob and Emma that the battle between hollowgasts and peculiars is much more complicated than they previously thought. Once in the building, Jacob and Emma discover a horrifying sight: some sort of medical room where peculiars—including some of their lost friends—are drained of their souls. They stop the procedure, saving a number of their friends, including Melina. Unfortunately, numerous other peculiars are still unaccounted for.
Fortunately, they discover the remaining peculiars imprisoned in the basement. After freeing them, the growing army of peculiars proceeds to a second prison cell where Miss Peregrine and the rest of her kind, female peculiars known as "ymbrynes," are detained. However, Bentham has betrayed Jacob and Emma. Bentham's wicked brother, Caul, a wight, is there waiting for Jacob. Caul wants Jacob to use his powers to locate the "soul jars" hidden in the Library of Souls. If Jacob refuses, Caul says he will unleash an army of hollowgasts upon them.
After a futile effort to fight back the hollowgasts, Jacob relents and is ferried by Caul to the Library of Souls, along with the peculiars and the ymbrynes, including Miss Peregrine. Seeing no other choice in the matter, Jacob uses his powers to locate the most potent souls in the library, which Caul and Bentham proceed to ingest. Doing so transforms them into giant monsters that, drunk with power, fight one another. Their brutal duel causes the library to collapse onto them, presumably killing them.
Miss Peregrine delivers Jacob and Emma to their homes. Jacob explains what happened to his parents, but Miss Peregrine proceeds to erase his parents' memory after the fact. Jacob and Emma write letters to one another frequently. Unfortunately, Jacob's parents discover one of Emma's letters and believe them to be further evidence of Jacob's insanity. Unaware of the truth behind Jacob's powers, his parents have always believed that their son suffers from mental illness. Desperate to stop Jacob's parents from sending their son to an insane asylum, Miss Peregrine visits Jacob's home and shows his parents proof that his powers are real. Miss Peregrine also reveals that the time loops governing the peculiars' existence—and preventing them from growing old—have been broken. This encourages Jacob and Emma to pursue a romantic relationship in earnest, now that they can expect to age like normal humans.