The three movies are each based on the same premise; there is a gigantic, mechanical, cube-shaped structure (the purpose and origin of which is almost completely unknown) that is made up of lots of smaller cube-shaped rooms. Each of these rooms has 6 doors, one on each wall and one on the ceiling and one on the floor, which lead into adjacent, identical rooms, only differing by color (green, blue, red, whilte). Some of these rooms are safe, while others are equipped with traps such as flamethrowers, acid and razorwire which kill the individual. The smart guys however use boots to throw into the rooms to detect the traps - however sometimes even this does not work as some of the traps are based on noise, motions etc...What must also be noted is that there are a number of serial numbers/letters that link each of the cubes - and they act as co-ordinates.
In each case, a group of strangers wake up in this mysterious structure, with no knowledge of how they got there or why they are there. In order to escape from the prison, however, they must band together and use their combined skills and talents to avoid the traps and navigate a way out of the maze (usually towards the cubes sides or theorized exits), while also trying to solve the mystery of what the cube is and why they are in it. However, the pressure of being in the cube also results in the group turning on itself.
Cube Zero was slightly different from the original two movies in that it also dealt with some people on the outside of the cube, technicians, whose job it was to control the cube and oversee those within. In this film it is suggested that the technicians believe that these people give their consent to be in the cube and that they are no more than condemned prisoners....but as the movie develops we learn that this is not the case. More questions than answers still remain....