There are shady characters at the spa, but only Mrs. Pargeter seems to notice and she is not concerned. She witnesses an overly thin girl being wheeled from the premises. She hires a detective to find some answers. The supposed decedent is an only child. The detective has the name of Truffler Mason. At the spa the Dead Sea Mud Bath treatment is based on a book. The difficulty with mud is keeping it muddy. The basement of the place is divided into cubicles for the mud treatment.
The boyfriend of the university student, the thin girl, is located. Eventually Mrs. Pargeter travels to Cambridge to interview some of the girl's fellow students. At the spa the customers aree dressed in Mind over Fatty Matter leotards. These costumes accentuate their bulges.
Mrs. Pargeter discovers an employee disabled by the mud and finds the response of the physician suspicious. Mr. Pargeter had been involved in questionable schemes and so Mrs. Pargeter's frame of reference is broad-based, liberal. It is discovered a whole line of goods has emerged from the concept of Mind over Fatty Matter. Mrs. Pargeter uses an investigative journalist to challenge the creator of the concept in search of clues to explain the doubtful scenes she has encountered at the spa.
Along the way it is discovered that the owner of the spa, Arkwright, acually belongs to a Rotary Club. It turns out an experimental treatment to alter body shape underlies the problems at the spa. The writing is accomplished and merry.