Hickory Dickory Dock

An outbreak of kleptomania at a student hostel was not normally the sort of crime that aroused Hercule Poirot's interest. But then he saw the list of stolen and vandalized items: a stethoscope, some old flannel trousers, a box of chocolates, a slashed rucksack, and a diamond ring found in a bowl of soup. He congratulated the warden, Mrs. Hubbard, on a "unique and beautiful problem."
The list made absolutely no sense at all. But, reasoned Poirot, if this was merely a petty thief at work, why was everyone at the hostel so frightened?
"When it comes to fiendish plotting, there's nobody to compare with Agatha Christie."