Unlike most of the novels featuring Byomkesh, this one does not involve any violent crime or major plot twists. The story revolves around the theft of a priceless heirloom, the "Seemanto-heera" or "Frontier Diamond", belonging to the heir of the Roy clan, one of the minor rulers of North Bengal. Byomkesh and Ajit have been invited by the current heir, a young Rai Bahadur Tridibendra Narayan Roy to recover the diamond. The diamond had been in the possession of the ruler for generations and a legend had been built around it. According to the legend, if the diamond were to ever be lost, then the line of succession would end. Tridibendran was the sole heir of his line according to the rules of succession where only the eldest son became ruler, but he did have an uncle, Sir Digindra Narayan Roy who was the younger brother of his father. Sir Roy was an established painter and sculptor who worked with mixed media such as plaster of paris. Sir Roy received a lavish monthly pension but since he wasn't heir-apparent, he did not get possession of the diamond. Consumed by greed, he did steal it while the diamond was on display in Calcutta and he replaced it with a fake that looked exactly the same to the untrained eye. He then notified his nephew that he had taken the diamond.