The Harts take a luxurious cruise on a Hart Industries liner to investigate a series of jewel thefts. They find themselves at the mercy of the jewel thieves' rival burglars.

Jennifer is mistaken for her look-alike, Dominique, and is kidnapped by ruthless killers. With the help of an unscrupulous columnist, the police, and the real Dominique, Jonathan devises his plan to save Jennifer.

Industrial espionage is a problem at Hartoy company. When the investigator Jonathan has hired is murdered, the Harts go undercover in an attempt to foil the crooks and save the company from financial destruction.

To strip mine the entire area, a ruthless mining tycoon is driving cattle ranchers out of business by poisoning the livestock via the stream that waters the properties. The Harts get involved when Jennifer's colt is poisoned.

Vince, a friend of Max's, arrives in USA to open a chain of health clubs. International criminals smuggle a solid gold barbell into the country with Vince's entourage.

The Harts' unscrupulous lawyer hires an assassin to eliminate Jonathan with plans to court and marry Jennifer and thus gain control of the sizeable estate.

The Harts visit the gallery of a well-known stamp collector to see the Vermillion, the most valuable stamp in the world. The Harts inadvertantly gain possession of the stamp and their lives are in danger.

A remote Island, an exotic European chateau, and a mysterious disappearance of an associate are not what the Harts anticipated when planning their romantic getaway.

While attempting to clear a friend of murder charges, the Harts become entangled in a disturbed woman's fantasies.

Jonathan's new suit has been switched with another. To save time he decides to make the exchange himself rather than through the taylor. At the other man's hotel room, Jonathan and Jennifer discover a body.

Art forgers are replacing masterpiece paintings with fakes and the Harts take action to trap them.

The Harts and Max are held at gunpoint when a murderer realizes that Jonathan has incriminating evidence linking him to the death of a champion skier.