A young psychic doesn't know she's an heir to a fortune (not a very good psychic, is she?) She also doesn't know she has a twin sister, until she has premonitions of a girl like her being murdered.
The Harts go under cover to solve this one. Jonathan pretends to be a trench-coated detective called "Marlowe" (get it?) but his Bogart impression isn't as good as his Cary Grant. Jennifer gets to play a flamboyant psychic with Max as ger assistant.
Fortunately, the suspect they're trying to nail believes in the Tarot and psychics and all that stuff.
This is really more like a Columbo episode: we have an idea early on who dun it; it's just a matter of getting the elusive proof. It's too bad for the victim but otherwise it's fun seeing the Harts play.