Plot Summary:With the British Prime Minister desperately seeking an absent Sherlock Holmes' assistance, the great detective's brother Mycroft steps in to solve the theft of the Mazarin Stone, a huge diamond taken in broad daylight from a museum display. The precious gem was soon to be returned to its original owners, the French, as a gesture of goodwill by Her Majesty's government. The inability to do so may now lead to a diplomatic incident. Using brother Sherlock's extensive files on society's criminal element, Mycroft soon focuses on Count Sylvius as the likely culprit. Dr. Watson has more time to spend in his surgery with his friend away but he is visited by two women with a mystery that would have been perfect for Holmes. They say their brother, who happened to be one of Watson's university professors, with a fantastic tale of a huge inheritance due them if only they can locate a third person that shares their own unique surname. As in turns out, the two cases are not unconnected.