With over 80 detective novels to her credit, not to mention an enormous number of short stories, plays and even romance novels under the pseudonym Mary Westmacott, Agatha Christie is, by any conceivable standard, a prolific author. Therefore, it follows as a logical inevitability that something she wrote must be classed as "the best" and something else as "the worst". I can't claim to have read everything the good lady wrote but, of those novels that I have read, "Passenger to Frankfurt" easily qualifies as the worst of the bunch.
Stafford Nye, a rather shiftless, easygoing member of Britain's diplomatic corps who, by his own admission, enjoys a good joke and takes life rather less than seriously, encounters a mysterious woman in the airport in Frankfurt. Appealing to his chivalrous instincts and his desire for a bit of an adventure, she persuades him to let her steal his passport and boarding pass and use them to travel to England to avoid what she claims would be her likely murder if she travelled to Switzerland on her previously intended route.
Starting from this preposterously unlikely opening scenario, Christie takes us on a pointless, meandering, achingly repetitive "thriller" that actually constitutes a personal diatribe - the aging dowager authoress's post 1960s current outlook on the world as she rather bleakly perceived it. Neo-fascism, youth rebellion, drugs, violence, armament smuggling, hippies, skinheads and megalomaniacal financial tycoons bent on world domination all make their appearance in a novel whose plot never truly crystallizes into anything concrete.
The current Wikipedia article on "Passenger to Frankfurt" quotes Robert Barnard, a crime writer and contemporary of Agatha Christie, who categorized this novel as "the last of the thrillers, and one that slides from the unlikely to the inconceivable and finally lands up in incomprehensible muddle."
I couldn't agree more. Not recommended.