Motivated by the successes of the ""Great Detective"" on whose television program they almost appear, Allison McNair (The Active-Enzyme Lemon-Freshened Junior High School Witch of 1973), her younger sister Jeannie, and her ""dumb, but trustworthy assistant"" Emmeline set out to track down the ""Perpetrator"" of a crime against Emmeline's father. It seems that Mr. Grant, an employee of the Newcharge Credit Card Company, may lose his job unless the person who is using his lost credit card is apprehended before the return of boss J. Hickory Haverstashe. The girls' sleuthing takes them along the path of the purchases to a variety of New York neighborhoods and shops, including sleazy Spiderella's Boutique where the thief purchased a red garter belt. They interview doormen and dogwalkers. They tail red herrings. And in the end, they find their prey. But the neurotic Perpetrator/victim is really not so funny and the situations and exertions of the girls are especially far-fetched.