You let the Milkman in, not knowing how much he liked you. He quietly stayed in your office after, watching you work.

You see another person walk up to the window as they pass their ID and entry pass under. They were a doppelganger, that would kill you if you let them in. But you didn't know that.. yet. They seemed to be a young lady, and she waited for you to unlock the door into the apartment. And your office.