

One of the members, Nick, explains that the group is not satanic. She initially tries to explain what has happened to the hospital staff, only to discover that she is once again in the clutches of the group. Terrified, Jules flees The Bartholomew, upon which point she is hit by a car and hospitalized.

This leads her to believe that the building owners are part of a satanic group called the Golden Chalice and that the missing people were used as sacrifices to lengthen their lifespans. Jules finds evidence to support this and grows even more suspicious after a sitter for another apartment, Ingrid, goes missing. She soon discovers that a woman named Erica Mitchell, who had previously stayed in apartment 12A before her, was very likely abducted for unknown reasons. While staying in the building, however, Jules learns that other people, predominantly apartment sitters, have gone missing in The Bartholomew. For Jules, this job is an opportunity to start over and live out a childhood fantasy. Jules's parents committed suicide by setting their home on fire shortly after Jane's disappearance. Jules's sister, Jane, also loved the book, but went missing years ago. Jules has always dreamed of living in The Bartholomew since her favorite book is "The Heart of a Dreamer" written by Greta Manville. She explains that they cannot let an apartment sit empty for more than a month's time, so as to deter burglars, and that Jules will live in the apartment until the family determines what they want to do with the unit. Leslie Evelyn is the woman in charge of hiring new tenants. With no job prospects, Jules answers a job posting for an apartment sitter for an upscale apartment in The Bartholomew after the death of its occupant. She lost both her job and her boyfriend, Andrew, and is now living with her best friend, Chloe, in New York City. This synopsis is in chronological order as opposed to book order.

The novel is set primarily during Jules's time in the apartment building and is interspersed with portions set during current day, when Jules has attempted to flee the building for reasons that become apparent as the plot progresses.

The novel made the New York Times Bestseller List for July 21, 2019. Lock Every Door is a 2019 thriller novel by American author Todd Ritter, writing under the pen name of Riley Sager.
