Having come later to the office, I intended to stay later. However, I took a break around 5PM to go across the street with the rest of the office. Our legal counsel has written a book, and so I walked over with the other interns to listen to the book reading and network. When I went back to work, I was initially perplexed because the building was locked! Then, with a stroke of genius (or rather, desperation), I swiped the card that allows me to access my office and it opened the door. It also made the elevator work. Phew. (Cue: "I got the power!")
When the custodian came by to empty our trashcans, I knew it was time to go home.