The man with the black hat is wanted, and you’re the only one who can take him down. For some reason you have to do it with a boulder.
You drive the hunter with the help of arrow keys and space bar. Use the arrow keys to move the chaser and to perform various actions over the subjects: use left or right arrow to push, throw and switch; use up or down to pick up and to put down, use space bar in other cases. The higher level is, the quicker the action is performed. Good luck in chasing the gangsters!