Something's Going On On This Train (S03E04)

Title: Trouble on the Express Plot: Hardcastle feels a mix of excitement and irritation when he's invited to a gathering aboard a private train, only to realize he’s been deceived into joining a deceptive journey with no stops for a day. Thankfully, Mark, who finds himself inadvertently stuck on the train as well, joins him in uncovering the truth. Their investigation takes a dark turn when a passenger is found dead. After the killer throws Mark off the train to escape suspicion, he cleverly returns to confront the situation. Following another murder, Hardcastle sets a cunning trap. While feigning to be a victim, Mark reveals Hardcastle had gathered incriminating evidence against the murderer. This leads the suspect, Carl Sharples, to expose his motive: a twisted vendetta against those he blames for his misfortunes. With Mark's assistance, Hardcastle intervenes just in time to prevent further tragedy.