Luke is on a school trip in Rome when he unwittingly becomes a suspect in an investigation to uncover a stolen painting. When the painting is returned for a small ransom, Luke becomes suspicious. What were the thieves really after? Luke does some investigating himself and uncovers a gang plotting to break a secret code that has obsessed treasure-hunters since the darkest days of the Second World War. Can Luke crack the code and get there first? What did the Nazis really hide in an unmarked cave in the Alps?