Penny Nichols and her friend Susan Altman attend a art show where the winning artist will receive a money prize. The majority of attendees feel the Black Imp piece is a sure winner, but are shocked when another piece is awarded the prize.

Later, Penny finds out that an original Rembrandt piece was stolen from the gallery on the same day as the show. Are the two incidents connected? Is there a connection to the the art critic Hanley Cron, who judged the art show and later accused the Black Imp's artist of being the thief of the missing painting? And what about Mrs. Dillon's missing pearls?

Being the daughter of a well known private eye and having solved a few cases on her own, Penny can't resist sleuthing to solve the mystery of the Black Imp and possible connections of the other mysteries.
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Let's face it -- Penny Nichols is pretty much Nancy Drew. With her roadster, her dead mother, her motherly housekeeper, and her supportive lawyer (I mean, detective) father, you could be forgiven for thinking this is really Nancy in the witness protection program. Not surprising, given that Joan Clark is really Mildred Wirt Benson, main author of the early Drew stories. As a Nancy Drew story, however, it's not bad.

Penny and her "plump" friend Susan attend an award ceremony at an art gallery, where they make the acquaintance of a young artist whose black imp sculpture is the popular favorite. When the award goes to someone else, she slips out early, before the discovery that a Rembrandt painting has been stolen from the gallery. Naturally she's the top suspect, and Penny works hard to keep the police from tracking her down (though they don't seem to think it's a problem to go shopping...)

Before the story is done, we encounter a copy of the black imp and a copy of the Rembrandt painting, every character we meet is implicated in the crime somehow, and Penny is tied up in a closet in a burning building. It's the classic Mildred Wirt Benson formula, and you get everything you expect.