One Late Night: Deadline starts off just before where the first game ends. You assume the role of a software engineer who is completely unaware of what has been going on during the night. He works at a company called Aeon Embedded, which has its offices in the same building. The building consists of 4 floors and all of the individual companies offices are locked and needs the proper keycards to open. You'll find these throughout the game.

The office complex is of modern architecture with steel beams, ceramic tile floor and parquet, a multitude of glass pane window walls, elevators, vending machines, kitchen/utility areas and various infomercial monitors. You will be frequently visiting the kitchen and utility areas (more on that below). The center of the complex consists of the open area lobby with stairs, elevators and walkways between the east and west wing of each floor. It's not exactly what you'd call a haunting or creepy environment, and at first glance it looks pretty unassuming, but alone at night in the gloomy lighting; you'll start to think twice.

The gameplay is objective based, meaning that at certain points through the game you will receive story objectives and also optional objectives. These objectives do not have to be completed in a linear fashion. A notification will appear on screen with a brief description of your new objective. At any time you can view (toggle) your current objective. Your main objective will be to investigate what has happened during the night and eventually the story will entwine with the story from the previous game as you find out more about the strange events.

As the story unfolds, you will meet some other people in the building that you will have conversations with. Additionally you will get to hear some voice acting from some of these characters.

"Deadline" will stay true to the original game with everyday office routines, and therefore you will from time to time visit the kitchen and utility areas to reduce your drowsiness level by drinking energy drinks and saving your game at the coffee and vending machines. The player is suffering from sleep deprivation from being overworked and this plays in a huge factor in the gameplay. Your drowsiness level will be increasing over time as you play the game and this affects your movement and vision and you may begin to see things that you are not sure if they're real or not. In the end you'll want to stay sharp if you want to finish your deadline.