The third part of the "Unsolved Case Code" series: 6 years ago, a bottle drifting on the sea was salvaged in Scotland, but the letter for help inside was regarded as an ominous thing, until an investigator accidentally saw the beginning of the letter written in Danish: Help! As Carl and his two subordinates cracked the code, they found that the author named "Paul" not only existed, but also disappeared after writing the letter in the bottle... Why didn't the boy's family track him down? Did he meet with an accident many years ago? Just as the investigation was stuck, a bizarre car accident exposed the flaws of the originally perfect evil crime. Carl, who had strung together all the clues, realized that what he was facing was not just an old case, but the desperate cries for help from many broken families over the past decade...