In the context of Joseph Campbell's framework called a "Hero's journey," which he described in his seminal work A Hero With a Thousand Faces, The Whispering Skull tells the story of a hero (Lucy) who goes on an adventure, completes that adventure and returns home transformed in some way. The Whispering Skull, like many novels in author Jonathan Stroud's series "Lockwood and Co.," follows Campbell's framework. The hero of The Whispering Skull is Lucy, a young woman who works with her friends in their Lockwood and Co. agency—an agency that is devoted to investigating and excising supernatural forces from the world. Together with her friends, Lucy and her friends go on two adventures: first, they investigate and attempt to eradicate ghosts that are haunting a school. They also go on an adventure when they are tasked with sealing Edmund Bickerstaff's grave and then deal with the fallout from their sealing his grave. Finally, after successfully finishing each adventure, Lucy returns home a changed woman. She learns more about the business that she is in and perhaps most importantly, more about herself.
Typically, novels for young adults are neither thematically complex nor filled with well-drawn characters. The Whispering Skull is an exception to that rule. It explores themes of the supernatural, how death plays a necessary (but sad) role in life, how rivalry affects people, allying with enemies, and the power of teamwork. Those rich themes give depth and add complexity to the story. They also propel the story forward, adding mystery and intrigue to the novel.
First, Lucy and her team at Lockwood and Co. are trying to stop the ghost of a man who had been executed nearly 200 years in the past from haunting a school. After arriving at the school, they discover that there isn't a single ghost haunting the school. Instead, dozens of ghosts are haunting the school. As a result, Lucy and her team retreat—but not before Lucy come inches from death.
Then, the next morning, Lockwood and Co. are asked by an enigmatic customer to seal Edmund Bickerstaff's coffin. After some initial trepidation, Lockwood and Co. eventually agree to take the case. They go to the man's gravesite, where Lucy's psychic powers are activated by the man's lifeless body (she calls herself a "listener" capable of detecting "psychic hum.") While looking over the man and his coffin before sealing it, Lucy hears someone in another realm say “Look! Look! [into the mirror in the man's coffin] You will find your heart’s desire!” Several of her team members fall for this ploy, causing them to be ghost locked, rendering them unable to move. A powerful and deadly spirit called a Source also gets loose due to a member of Lockwood and Co's mistake. That Source is the namesake whispering skull, which almost immediately starts speaking to the group. The skull, however, pays particular attention to Lucy because of her psychic abilities.
Meanwhile, an investigator from the Department of Psychic Research and Control orders Lockwood and Fittes to find the mirror which was in the man's coffin. Their work to try and obtain the mirror begins in earnest, with help from the Whispering Skull. And they very quickly find the mirror but smash it rather than return it to the government agent. Lucy was advised to smash the mirror by the Whispering Skull.
As a result of her actions and her fearlessness in the face of tremendous danger, Lockwood decides never to keep secrets from his cherished employees anymore. He takes them to a secret room which he had previously told them was forbidden. There, they learn things they never knew before, including about other demons, which sets the stage for the next novel in the series.
