Plot hole: When Nick confronts the P.I. and yells "Why are you following me?", he looks inside the car and see the file with his picture on the front seat. The P.I. notices this and turns the file over. After Nick grabs his gun, the P.I. jumps out on the other side, raises his hands in the air and tells him somone hired him and runs off. As the P.I. runs off, Nick yells "Who hired you?" as he stands alone next to the car. He then waits a minute and walks off. If he really wanted to know more information, he could have taken the file that was right in front of him on the carseat. It makes no sense that he is desperate for information about the strange events that are going on, sees this file on him, and yet doesn't even pick it up or look at it.
Plot hole: At the end, when Nick is on the roof and everyone is behind the metal doors, you hear the saws trying cut through the door and the sparks flying. Immediately when they cut through, the doors swing open and everyone is standing right up front with Champagne glasses. No one is holding any saws or equipment or have any in front of them. Nor was there was any time for the people cutting the doors to run to the back to hide behind everyone else since the sparks fly right up until the doors swing wide open.