Although Hardcastle is initially pleased to be invited to a party on a private train, his emotion changes to anger when he discovers that he has been lured onto the train under false pretenses. His ire is further raised upon discovering that the train is not scheduled to stop for another day. One small consolation: Mark, accidentally trapped on board the train, is around to help him find out what is going on with the trip. The mystery takes a deadly turn when one of the passengers is murdered. Although the unknown murderer temporarily manages to get rid of Mark by throwing him off the train, the ex-race car driver, who is unable to identify his assailant, pools his resources and returns to the train down the track. Another murder prompts Hardcastle to set a trap for the killer. While Hardcastle pretends to be a victim, Mark purposely lets slip that the judge had obtained evidence against the killer. Taking the bait, passenger Carl Sharples tries to search Hardcastle's "body". Exposed a