The following version of the book was used to create this study guide: Stroud, Jonathan. The Screaming Staircase (Lockwood & Co. Book 1). Hatchette Book Group, New York, NY, 10104. 2013. Kindle AZW file.

Lucy Carlyle lives in England about 50 years after ghosts have become a daily presence. While some are harmless, some are angry and dangerous. People do not want to interact with any of them. This has given rise to the formation of agencies that specialize in investigating ghosts and eliminating the Source of their presence, thereby eliminating the possibility of a terrible interaction between that ghost and a human. One major element of this situation is that only youngsters can clearly detect the ghosts. Lucy is one of the youngsters with that ability. She hears ghosts more clearly than she sees them. She is the youngest child of an impoverished family and takes a job working for a ghost agent in her home town when she is only nine. When the six children working for Agent Jacobs are tasked with investigating a haunted mill, Lucy feels an increased danger but cannot provide concrete evidence. The other five children die, and Lucy leaves home to find a job in London where she answers an advertisement from Lockwood & Co.

Lucy is greeted by Anthony Lockwood and George Cubbins. Though she becomes annoyed when they test her ability to detect the ghostly presence of several items, Lockwood hires her on the spot, and Lucy moves into the attic of Lockwod's home. The three youngsters live and work alone. There are some clashes, especially when Lockwood and Lucy want to rush into situations without waiting for George's research. This happens when Lockwood and Lucy go to the home of Mrs. Hope. They expect to find that the ghostly manifestation haunting Mrs. Hope is that of her late husband. Instead, they discover the ghost of the young actress Annabel Ward. She is filled with a level of fury that catches Lucy and Lockwood off guard. When they find her body in the wall and cover it with a net, they assume they have eliminated the Source of Annabel's presence. During the confrontation, Lucy and Lockwood set Mrs. Hope's house on fire. They are later confronted with a demand for payment for the damages. Lockwood says they have no way to pay other than selling his house.

They are surprised when Annabel's ghost arrives in Lucy's bedroom until Lucy realizes she had impulsively grabbed the locket from Annabel's body before the fire forced them out. Armed with Lucy's belief that the person who gave Annabel the necklace is her killer, they set out to solve the mystery in the hope of increasing business.

In the midst of this investigation, Mr. John William Fairfax arrives at Lockwood & Co. He offers an incredible amount of money if the three will come in two days to investigate his haunted estate. While Lucy puts together their supplies, George hurriedly does research. By the time they arrive at Combe Carey Hall, Lockwood has a vague theory about Annabel's murder and about Mr. Fairfax. Lockwood, Lucy, and George discover the Source of the haunting – the bones of seven murdered monks in a well at the bottom of a Screaming Staircase. By that time, Lockwood has put together some other clues and realizes Mr. Fairfax expected them to die during the investigation. He is trying to cover up the fact that he killed Annabel in a moment of jealous rage. Lucy has been carrying Annabel's locket in a special container on a cord around her neck, and she decides that Annabel is their only hope. When Lucy opens the container, Annabel kills Mr. Fairfax.

In the aftermath, Lockwood & Co. is the subject of positive articles in the paper, ensuring the agency's survival. Lockwood questions Lucy, asking if Annabel had communicated with her directly. Lucy denies that claim, which is believable since only one other ghost agent has ever been able to communicate directly with ghosts. When Lucy goes to the basement storeroom to get doughnuts for their celebratory dinner, she stumbles and releases the tap on a ghost-jar George keeps for experiments. The ghost inside calls Lucy's name. He says she is different from the others and predicts something terrible is coming. Lucy closes the tap, knowing that this night is just for celebrating with Lockwood and George.