At the end of the last episode, Jimmy uncovered the missing jewels that had been stolen. Unknown to him and Clark, the Yellow Mask has entered the train in pursuit of the jewels.
Today the girl who had her train window smashed is interviewed by the Mask, as he is disguised as a police detective. Through the interview, it’s revealed that the former rivals of the Yellow Mask are on board the train, Clark Kent and Jimmy Olsen. Seeing his chance when Jimmy is left alone, the Mask kidnaps him to try to learn what happened to the jewels.
Where is Clark? As Superman, he is doing his own investigating, and has left the train where he learns of the Yellow Mask’s involvement. Now he has to rush back to the train to protect Jimmy. If he can.