The novel is set some time during the Cold War, and features a spy fiction sub-plot, narrated in first person by Colin Lamb, a British Intelligence agent trying to track down a spy who has been passing information to the enemy. Colin's investigation brought him to the scene of a rather peculiar murder case, in which an unknown man was found stabbed in the house of Miss Pebmarsh, a blind woman. The man carries no identification with him, and no one seem to recognise him. His body was discovered by Sheila Webb, a typist who was apparently hired by Miss Pebmarsh, although the latter denies making such appointment. Colin then brings the case to Poirot, who agrees to investigate the murder through Colin's written accounts.
In 2010, ITV adapted the story for the 12th season of Poirot.
This novel provides examples of the following:
- Crazy Cat Lady: Mrs. Hemming, occupant of 20 Wilbraham Crescent, owns about 20 cats, and can't seem to talk about anything but cats.
- Decoy Protagonist: Colin may initially seem like The Protagonist, being the "outsider" who stumbles into the crime scene and was dragged into the subsequent investigation. However, his role in the case was secondary to Hardcastle. Even the suspects they interrogate see him as nothing more than Hardcastle's extra hand.
- Dirty Commies: Colin is in the neighborhood to investigate possible Soviet agents transmitting intelligence back to Moscow.
- Everyone Can See It: Inspector Hardcastle, Poirot and Colonel Becks (Colin's superior) all realise that Colin has fallen hard for Sheila due to his obstinate conviction that Sheila is innocent. Colin himself insisted that he has a perfectly logical reason for believing her innocence, and did not admit that he has less-than-professional feelings towards her until halfway through the book.
- First-Person Peripheral Narrator: Zigzagged. Colin is only tangentially involved in the murder investigation, and barely makes any contribution in the interrogation of suspects. However, he's an undisputed lead of his own sub-plot. On the other hand, the first-person accounts only make up less than half of the actual narrative, while the novel is mostly written in third person.
- Hero of Another Story: Despite being the (occasional) narrator of the novel, and whose accounts of the investigation is what led Poirot to the solution of the mystery, Colin's main concern is to find The Mole who has been selling British secrets to the Soviets, a spy sub-plot that is somewhat glossed over in the actual events of the books.
- Love at First Sight: Sheila Webb runs into Colin Lamb, and the latter immediately declares her as "his" girl.
- Luke, I Am Your Father: Miss Pebmarsh is revealed to be Sheila's Missing Mom, although Sheila is never told of this fact.
- Motor Mouth: Nora couldn't stop talking, to the amusement (and sometimes annoyance) of her co-workers.
- Parental Abandonment: Sheila lives with her aunt, who tells her that her parents is dead. In truth, she's an illegitimate child. Her mother, Mrs. Lawton's sister, gave her up because she was an ambitious woman who doesn't want a child to hinder her career.
- Phone-In Detective: Poirot never sets foot in the crime scene, nor does he actively take part in the investigation. He makes all his deductions based on Colin's written reports.
- Red Herring: The titular clocks are not as important to the plot as one would believe them to be.
- Ripped from the Headlines: Inverted in-universe. The killer used an unpublished mystery novel manuscript as the basis of their murder scheme.
- Shout-Out: Colin visits a girl who lives across the street from the murder scene who, confined to the apartment with a broken leg, passes the time watching her neighbors. Sound familiar?
- Two Lines, No Waiting: Two separate investigations were taking place in Wilbraham Crescent. One is of the murder scene in Miss Pebmarsh's home, and one is an espionage plot where one of the occupants of the neighbourhood is believed to have been passing national information to the enemy. Aside from the fact that they take place in the same location, and has Colin's involvement, the two plots are not actually related to one another. Though it is worth noting the address Colin has been given to investigate the spy ring houses the murderer (well, some of them), and the house where the body was found is home to the spy Colin is searching for.