This is the first part of the trilogy featuring prisoner 1213 (Twelve Thirteen). Locked up in a dark cell and consumer by sickness, the prisoner has got no idea where he is and how he got there. He is addressed as 1213, the number of his cell, and every day a bespectacled man takes him through an obstacle course to test him. One day, the door suddenly opens with no apparent cause and 1213 takes the chance to escape.
1213 is an action platformer with lots of puzzle elements. With gameplay and movement similar to Flashback and the original Prince of Persia, the player has to help 1213 find a way out. Armed with a gun with an unlimited amount of bullets, 1213 is able to move around, crouch, jump, dangle on ledges and shoot enemies. No more than one item can be carried around at all times. Consoles contain logs that provide insight into the background story. To progress, 1213 has to shoot enemies and solve various puzzles that require more thought than in regular platform games.
1213's remaining life is represented by a beating heart in the top left hand corner. The faster it beats, the less life left. It can be turned back normal by showering.