You are the guard of a bank with 12 doors. You may look at three adjacent doors at a time.
Through the doors clients come to deposit their money, but bandits try to enter too. You must shoot the bandits before they shoot you.
You lose a "life" if shot by a bandit or if you shoot an innocent (bombs appearing from doors and the time limit can also kill you).
You complete a level once the bank has earned money from all the doors.
If you are not defeated (losing all lives), the game goes on indefinitely (there's no "final victory", you simply try to score as many points as you can while reaching just another level).