Lock Every Door is a 2019 thriller novel by American author Todd Ritter, writing under the pen name of Riley Sager.

The plot concerns an apartment sitter at an exclusive building in Manhattan who discovers that her predecessor in the job disappeared under suspicious circumstances.

Property manager and longtime resident Leslie Evelyn explains that the former occupant has died, but they cannot let an apartment sit empty due to fear of burglars.

Jules moves in and meets the other residents, including fellow sitters Dylan and Ingrid, handsome "Dr. Nick," and the irascible author Greta Manville, whose novel features The Bartholomew on its cover.

Jules learns the building has a checkered history, including the murder of a servant girl by another resident, the suicide of the original builder, and the disappearances of other apartment sitters.

Combining Ingrid's knowledge with her own research, Jules comes 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.

[5] Lock Every Door received reviews from outlets such as the Wall Street Journal and NY Journal of Books, the former of which stated that Sager "relates ominous events and spooky developments with skill, adding an element of social commentary and a surprise twist ending—elevating this exercise in terror above the ordinary shocker.