The Theft of the Royal Ruby (S03E09)

In a London restaurant a drunken young prince staggers after his female companion who has stolen his priceless ruby. Poirot is briefed by the Foreign Office about the theft of the gem belonging to the petulant heir to the King of Egypt. Persuaded to take on the case in the national interest, Poirot is told he must spend Christmas at the home of one of the only people who knows about the precious stone - Egyptologist Colonel Lacey. (iTunes)