Summary: Even though Darrin's spirits are up, his sales are down and Larry urges Samantha's mate to take a week off to stir-up the creative juices. Darrin comes back to work and readies himself to face one of the agency's meanest (and richest) customers. Mr. Harmon clearly makes it known that he has thus far been dissatisfied with Larry's choice of ad campaigns. Looking to Darrin for something extra special, he is pleased when he comes up with a concise, well directed sales pitch that he's certain Mr. Harmon will applaud. Instead of clapping, Mr. Harmon turns thumbs down on the entire ad campaign. Darrin can't understand what went wrong. He can think of no mortal reason why it happened and he concludes it must be witchcraft.
Certain that his meddlesome mother-in-law put a zap on his creative sap, Darrin asks Samantha to counter-zap her mother with a favorable twitch. Sam concocts what she says is a magic potion that will give her harried husband the confidence he needs to sell himself and his ideas to Mr. Harmon. Suggesting that he take the very same ad campaign which was rejected back to Harmon, Darrin drinks the juice and is instantly a man of confidence. To Larry's great shock, Darrin sells Mr. Harmon the very same ad campaign he rejected yesterday. To Darrin's great shock, Samantha informs him that his confidence was his own and that the potion that he drank had no more zap than soda pop.