Help on a Baseball question?

bases are loaded. No outs! The batter hits an inflield fly at the shortstop. The runner on First runs, thinking the ball will drop. He passes the runner on Second. The base umpire indicates that the infield fly is in effect on the play. The ball then falls and hits the runner on Second as he is attempting to catch up with the runner who was on First at the time of the pitch! The runner on Third, sees the approaching runners and decides to attempt to take Home. He then, decides to return to Third and makes an illeagal slide into the Third baseman! The shortstop picks up the ball and has no idea where the play should be made! What is the appropriate call?