Samantha doesn't want Darrin to know that she bought a new coat as he will probably think the purchase too frivolous for their budget. Darrin does find out, and although he reluctantly allows Samantha to keep the coat, Samantha vows to take it back. Endora is appalled by what she sees as Samantha needing to live on a budget, which she attributes to Darrin's cheapness. As such, Endora places a spell on Darrin to make him the most miserly person in the world. Not only does the spell affect whether Darrin allows Samantha to keep the coat, it affects Darrin's working relationships, especially with Larry, who wants to charge clients to the max, and their latest client, Mr. Bigelow, who is the tightest tightwad in the world. Samantha quickly surmises that Darrin's recent cheapness is all Endora's doing. So while Samantha tries to get her mother to remove the spell, she concurrently tries to undo the spell herself during a business dinner with Bigelow, with unintended consequences.
—Huggo