An English pilot for a Middle Eastern ruling prince just managed to hide a fabulous fortune in gems somewhere in his sister's room, just before the prince was overthrown in a revolution. The unsuspecting sister returned to England with her daughter, just in time for the girl to start in Meadowbanks, an elite girls school, where a female cousin (& fiance) of the deposed prince, was also arranged to attend.
Several interested parties had been on the prowl searching for the gems, the pilot's efforts had not been as clandestine as he had hoped. With new girls, new teachers, and also a new young handsome male gardener, was it a wonder that some residents of Meadowbanks felt as if there was a hidden cat among the pigeons.
Agatha Christie painted an excellent picture of an English public school going about its daily business. There were staff as well as students who were trying to get use to a new environment. There was a headmistress, who having successfully established the school according to her vision after years of struggle, was considering passing the torch to the next generation. There were old faithfuls among the staff who were less prominent but had heard and seen much of what others missed.Meadowbanks was probably Agatha Christie's of what an ideal school should be like.
Having got the background set, Agatha Christie got down to business with the first murder, the victim being a rather unpopular new staff in the recently completed Sports Pavilion. Readers would have been given enough outright hints before this as to what would be of interest in the Sports Pavilion. The object of the mystery quickly turned from recovery of the gems to the discovery of the murderer.
Midway, a second murder almost threw the investigators off-track, and a third murder was committed before Hercule Poirot who was called in late in the game seriously got down to business. Mystery readers could find little fault in way which the authorities set about trying to find the culprit, but it took bringing back a student's mother from Anatolia to trap the murderer.
All the while, Christie managed to maintain a light hearted atmosphere despite the deaths in the story, with occasional injection of humour and wit. She included important and interesting roles for the diverse characters from students to faculty to police to parents in how the mystery was played out. This is truly one of her most readable book.