TRIO: The Kepler Diamonds

Legend has it that the world's most valuable diamond treasure was hidden inside Hamburg's city walls almost 500 years ago. Treasure hunters have searched in vain, but no one has yet found "The Kepler Diamonds". A coin is claimed to be the key to cracking the code. Eight years ago this coin was stolen from a museum. It has not been seen since ... There is an attempt to kidnap Nora, and slowly but surely it appears that her father, who she thought was dead, must still be alive. He is held captive by treasure hunter Schwartz. The treasure hunter believes that Nora's father knows where the coin is and wants to kidnap Nora to force him to hand over the coin.