Extend the Story - Add a Room

You decide to open the Briefcase. You pull the levers at the front to the sides, and the lid pops open. Here you lift the lid, and find concealed inside a Sniper Rifle with a Suppressor and two .45 Pistols also with suppressors. With the weapons, there is also a note. You unfold it and read:
"If you are reading this note, it means you have lost your memory. The only way for this to have happened is if you were Captured whilst on a mission. if you want to find out everything before the "accident," go to the Public Library at 45 O'neill Street.
P.S. If there are men at the door, make your escape through the Bath in the Bathroom. Just lift it and go from there, and don't forget to take the Briefcase with you."

You finished reading the note, so you tore it up, and closed the Briefcase. From here, you went to the Cupboard and grabbed a large Trench coat.
From here, you followed your advice and went to the Bathroom, lifted the bath, and went underground. Then the room began to shake, followed by a extremely loud bang, and gunfire.

Pull out your weapons and stand your ground