The story that was laid out (or obscured, in some cases) in the demo followed the player haunted by a ghost in a constantly shifting, inescapable hallway. A radio broadcast in the hallway discusses a father who murdered his family before taking his own life. The player is then continually confronted by a female ghost (Lisa) who is often sobbing when she's not accompanied by the cry of her infant.
The player gets a long look at this "infant" when trapped inside a bathroom, but you never get to linger anywhere too long lest the one-eyed, rotting ghost of Lisa snaps your neck. Most of the time you can hear her behind you, but turning around reveals that it was all in your head. Well, almost.
Lance McDonald set out to prove that Lisa was there all along. He hacked the demo to place the game's camera, which is usually set in a first-person view point, into a stable position. He then moved the player's character forward without turning around to reveal Lisa is in fact behind you.
In P.T., it's common to hear noises as if Lisa is right behind you, or see weird shadows moving around in front of you, but when you turn around, there's nothing there. I hacked the game to allow the player to see behind them without actually turning around and... pic.twitter.com/bj1P0ymIZ6— Lance McDonald (@manfightdragon) September 9, 2019
She actually attaches to the player's back as soon as you get the flashlight, here, I demonstrate how you can see some strange shadows. I then lock the camera in place and walk forward, showing how she's always there... following you... pic.twitter.com/zarhwjNmZz— Lance McDonald (@manfightdragon) September 9, 2019
McDonald is promising to reveal more content hidden in the depths of P.T., hopefully in time for Halloween season.
Source: Lance McDonald's Twitter account