The Secret Adversary (Tommy and Tuppence Series)

A man's voice beside her made her start and turn. She had noticed the speaker more than once amongst the first-class passengers. There had been a hint of mystery about him which had appealed to her imagination. He spoke to no one. If anyone spoke to him he was quick to rebuff the overture. Also he had a nervous way of looking over his shoulder with a swift, suspicious glance.
She noticed now that he was greatly agitated. There were beads of perspiration on his brow. He was evidently in a state of overmastering fear. And yet he did not strike her as the kind of man who would be afraid to meet death!