With Lock Every Door, Riley Sager deviates slightly from the themes of his first and second books but maintains the same fast pace and unexpected twists that give such a satisfying read. Jules lost her sister eight years ago, but she isn't necessarily trying to unravel a mystery from her past. Instead, she's simply struggling in the present. When offered a chance to apartment sit at the Bartholomew she takes it, despite the rules being a little on the sketchy side because the benefits outweigh any suspicions. But then other apartment sitters go missing. And sometimes she thinks someone else might be inside the apartment she's staying at. Is it a ghost? Something more sinister? Jules begins to dig into the past of the Bartholomew in order to find answers. Just like Jules, if you think you have those answers figured out, I guarantee you're wrong.