As the title suggests, you're supposed to find out who shot singer Johnny Rock (or at least who hired the guys who shot him) and put them behind bars.
There are some differences between this game and previous American Laser Games shooters. Instead of a wimpy pistol, you get a tommy gun (which doesn't need to be reloaded). Unfortunately, you also have limited ammo and need to buy more at times. Instead of lives you have a fixed supply of money, and each time you die you lose some cash. Lose it all and it's game over.