Karen Shields (Karen Austin) is the villainess from Hart to Hart episode 01X09 "A New Kind of High". In this episode, two chemists (Karen Shields and her male assistant David) at one of Jonathan's subsidiaries have developed a new hallucinogen. Karen, who clearly controls the duo, wants to sell it as a powerful new narcotic on the drug market in order to make a lot of money.
For that purpose, she's ready to eliminate all of those who may interfere with her plans.
Their supervisor, Dr Capello, is her first victim when he find out the truth about their intentions and try to contact Jonathan Hart by phone during the night to report them. Karen and David enter in his office at this moment and there is a discussion which ends with him dismissing them and Karen pulling out a firearm from her purse. After a brief chase in the deserted research centre, she discovers his hideout and teases him while he begs for mercy. The killing itself isn't shown but is probably done with her firearm. Anyway, they then transform the crime scene into an accidental explosion due to a wrong chemical manipulation from the supervisor.
Jonathan Hart, however, have suspicions and his investigation become a problem for them. Karen attempts to kill him by drugging his coffee before he takes his car, but Jennifer Hart, also present in the car, manages to regain control of it and prevent a serious accident.
Then, Karen and David are seen on a parking concluding a contract with a sort of drug lord which makes them rich... and which makes David useless to the evil Karen. After the contractor has left, she pulls out her firearm and coldly executes her former lover. Then she returns to the research centre in order to collect the chemical formula of this new hallucinogen.
Finally, Karen surprises Jonathan and Jennifer searching and finding a proof against her in a weather simulation chamber of the deserted research centre. From the control room of the weather chamber, she locks the automatic door and sadistically decide to subject them to brutal and swift temperature changes.
Taking apparently a great pleasure in tormenting her former employer and his wife before killing them, she first plays with the wind mode which makes them flying across the chamber. Then she cuts the storm, activates the snow mode and gradually decreases the chamber temperature until -60°F (-50°C).
She finally decides to finish them off by gradually increasing the temperature with the chamber heat lamps, while Jonathan is desperately trying to open a steel plate under her observation window with a nail file.
When the temperatures reaches something like 160°F (70°C), and against all expectations, Jonathan finally manages to open the steel plate at the very last moment and creates a short circuit which electrocutes Karen, shuts off the weather chamber and unlocks the automatic door, allowing Jonathan and his wife to escape.
The fate of Karen is unknown, but since the electrical shock didn't seem to be lethal but only knocked her out, she probably was arrested by the police and sent to jail.