George Abbot is an alleged British commercial agent and frequent traveler on the Orient Express to conduct his business across the continent. In truth, he is an agent of MI6, investigating the presence of terrorists on the Orient Express.
He is a last-minute addition to the train as he boards the train at Munich. His name doesn't appear on the passenger list. He appears talkative and inquisitive, chatting with almost everyone he comes by. With a sharp, capable mind, he can be in the right place at the right time and know a lot of personal information.
After the murder of the young Alexei Dolnikov, he reveals to Robert Cath that he was aware of his true identity, along with his exploits concerning the Irish incident and his impersonation of Tyler Whitney and offers him to work with the British government for the upcoming European crisis.
He is one of the few characters who actually make it to Constantinople.