An outbreak of kleptomania at a student hostel is not normally the sort of crime that arouses Hercule Poirot’s interest. But when he sees the bizarre list of stolen and vandalized items – including a stethoscope, some old flannel trousers, a box of chocolates, a slashed rucksack and a diamond ring found in a bowl of a soup – he congratulates the warden, Mrs Hubbard, on a 'unique and beautiful problem’. And, reasons Poirot, if this is merely a petty thief at work, why is everyone at the hostel so frightened?