Daisy Wells and Hazel Wong are taking a holiday through Europe on the world-famous Orient Express. From the moment the girls step aboard, it's clear that each of their fellow first-class passengers has something to hide. Even more intriguing: rumour has it that there is a spy in their midst. then, during dinner, a passenger is found murdered in her cabin and her stunning ruby necklace gone. Daisy and Hazel are faced with their first ever locked-room mystery -- and with competition from several other sleuths, who are just as determined to crack the case as they are.