The Final Enemy. An Inspector Faro Mystery No.12.

1889. Faro's plans to meet his companion Imogen Crowe in Germany are shattered by a Royal command to escort Prince George of Luxoria from boarding-school in Scotland back to his strife-torn country. With assassins in pursuit even the Orient Express cannot guarantee their survival and Faro has a deeply personal reason for ensuring the prince's safety - a secret concerning his birth that could destroy them both. (See 'The Missing Duchess') .