Lock Every Door by Riley Sager (Paperback)

They've offered you a luxury apartment, rent free. THE CATCH: you may not live long enough to enjoy it...

No visitors. No nights spent away from the apartment. No disturbing the other residents.
These are the only rules for Jules Larson's new job as apartment sitter for an elusive resident of the Bartholomew, one of Manhattan's most high-profile private buildings and home to the rich and famous.

Recently heartbroken and practically homeless, Jules readily accepts the terms, ready to leave her past life behind.

Out of place among the extremely wealthy, Jules finds herself pulled toward other apartment sitter Ingrid. But Ingrid confides that the Bartholomew is not what it seems and the dark history hidden beneath its gleaming facade is starting to frighten her. Jules brushes it off as a harmless ghost story - but the next day, her new friend has vanished.
And then Jules discovers that Ingrid is not the first temporary resident to go missing...

Welcome to the Bartholomew...You may never leave