Daisy Wells and Hazel Wong are taking a holiday 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, there is a scream from inside one of the cabins. When the door is broken down, a passenger is found murdered, her stunning ruby necklace gone. But the killer is nowhere to be seen - as if they had vanished into thin air. 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.