Puzzle Room: Operation KFC

It is the year 1938, the possibility of a war with Germany is getting closer and therefor Czechoslovak leaders decide to transfer the coronation jewels from the Crown Chamber of St. Vitus Cathedral to a safer place. Operation KFC (jewels of fascinating price), as the event was called, aims to get jewels to the bank vault in Slovakia. However, a road accident occurs during the journey and one of the coronation jewels is forever lost. Or is it not forever......? Can your team solve the thief's rediscovered notes and discover a lost gem?