Due to an airline strike the Harts have to travel from Chicago to Los Angeles by train. They unwittingly get caught up in a murder plot involving other passengers.
To catch a group of counterfeiters who murdered an investigator, Jennifer and Jonathan go on a cruise, she posing as a European countess and he working as a ship's steward.
When Jennifer overhears an acquaintance and his mistress planning to murder his wife on the ski slopes, she and Jonathan jet off to Vail to prevent it -- but are they too late to save her on the ski trail?
Max has been taken hostage in order to train two Hart look-alikes to fool some wealthy people at a dinner. In a case of mistaken identity, the real Jonathan and Jennifer turn up, unaware of what is planned for them.
After witnessing a murder, Jonathan hits his head and loses his memory. As he tries to recover his memory, he starts to suspect he may have had a mistress -- and killed her.